[Security Solution] Refactor prebuilt rule customization test plans, …

…part 3 (elastic#212420)

**Epic:** elastic#174168
**Partially addresses:**
elastic#202068,
elastic#202078,
elastic#202079
**Follow-up to:** elastic#211472

## Summary

We're cleaning up and refactoring our existing test plans for prebuilt
rule customization, upgrade, and export/import workflows.

Specifically, this PR:

- Updates the common structure of test plans:
- Adds a tip to each test plan's header to help with navigating all our
test plans for prebuilt rules.
- Introduces a new `Requirements` section to each one and consolidates
assumptions, technical requirements and product requirements under it.
- Each `Product requirements` section now contains relevant user stories
and other product details. In the document flow this is kept close to
the `Scenarios` section.
  - Updates the test plan template according to the updated structure.
- Moves the documentation about customizable and non-customizable rule
fields to the common info document.
- Restores the lost changes from commit
elastic@bde4612.

No "functional" changes have been made to any test plans, such as
adding, removing, or updating any scenarios. The only functional-like
changes were made to the user stories when creating/updating the product
requirements sections.

This PR wraps up the refactoring efforts aimed to prepare the test plans
for being "functionally" changed and improved in follow-up PRs. In the
following PRs, we're going to cover the logic described in
elastic#210358, address any gaps in the
coverage, and improve the scenarios structure and wording.

## Review tip

It might be easier to review this PR commit-by-commit as each of them
contains logically cohesive changes.

x-pack/solutions/security/plugins/security_solution/docs/testing/test_plans/README.md

@@ -37,6 +37,6 @@ Each subdomain folder should be owned by a single GitHub team in the `.github/CO
 Some examples for reference:
 
 - [Test plan template](./test_plan_template.md).
-- [Installation and Upgrade of Prebuilt Rules](./detection_response/prebuilt_rules/installation_and_upgrade.md).
+- [Test plans for prebuilt rules](./detection_response/prebuilt_rules/prebuilt_rules.md).
 
 Feel free to tune the structure whenever it makes sense and improves readability or maintainability of your plan: add more sections to `Useful info`, add more top-level sections in addition to `Useful info` and `Scenarios`, etc.

x-pack/solutions/security/plugins/security_solution/docs/testing/test_plans/detection_response/prebuilt_rules/prebuilt_rule_customization.md

@@ -2,6 +2,9 @@
 
 **Status**: `in progress`, matches [Milestone 3](https://github.com/elastic/kibana/issues/174168).
 
+> [!TIP]
+> If you're new to prebuilt rules, get started [here](./prebuilt_rules.md) and check an overview of the features of prebuilt rules in [this section](./prebuilt_rules_common_info.md#features).
+
 ## Summary <!-- omit from toc -->
 
 This is a test plan for the workflows of customizing prebuilt rules via:
@@ -24,10 +27,11 @@ https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one
 
 - [Useful information](#useful-information)
   - [Tickets](#tickets)
-  - [User stories](#user-stories)
   - [Terminology](#terminology)
+- [Requirements](#requirements)
   - [Assumptions](#assumptions)
-  - [Non-functional requirements](#non-functional-requirements)
+  - [Technical requirements](#technical-requirements)
+  - [Product requirements](#product-requirements)
 - [Scenarios](#scenarios)
   - [Editing prebuilt rules](#editing-prebuilt-rules)
     - [**Scenario: User can edit a non-customized prebuilt rule from the rule edit page**](#scenario-user-can-edit-a-non-customized-prebuilt-rule-from-the-rule-edit-page)
@@ -60,9 +64,35 @@ https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one
 - [Users can Customize Prebuilt Detection Rules: Milestone 3](https://github.com/elastic/kibana/issues/174168)
 - [Tests for prebuilt rule customization workflow](https://github.com/elastic/kibana/issues/202068)
 
-### User stories
+### Terminology
+
+- [Common terminology](./prebuilt_rules_common_info.md#common-terminology).
+- **Rule source**, or **`ruleSource`**: a rule field that defines the rule's origin. Can be `internal` or `external`. Currently, custom rules have `internal` rule source and prebuilt rules have `external` rule source.
+- **`is_customized`**: a field within `ruleSource` that exists when rule source is set to `external`. It is a boolean value based on if the rule has been changed from its base version.
+- **non-semantic change**: a change to a rule field that is functionally different. We normalize certain fields so for a time-related field such as `from`, `1m` vs `60s` are treated as the same value. We also trim leading and trailing whitespace for query fields.
+
+## Requirements
+
+### Assumptions
+
+Assumptions about test environments and scenarios outlined in this test plan.
+
+- [Common assumptions](./prebuilt_rules_common_info.md#common-assumptions).
+- Rule package used will have all previous rule versions present (no missing base versions).
+
+### Technical requirements
+
+Non-functional requirements for the functionality outlined in this test plan.
+
+- [Common technical requirements](./prebuilt_rules_common_info.md#common-technical-requirements).
 
-**Prebuilt rule customization workflow:**
+### Product requirements
+
+Functional requirements for the functionality outlined in this test plan.
+
+- [Common product requirements](./prebuilt_rules_common_info.md#common-product-requirements).
+
+User stories:
 
 - User can edit a single prebuilt rule from the Rule Details page.
 - User can edit single prebuilt rules one-by-one from the Rule Management page.
@@ -76,22 +106,6 @@ https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one
 - User can see which rules are customized on the Rule Management page in the Upgrade table.
 - User can un-customize a prebuilt rule by editing it and reverting its parameters back to their original values.
 
-### Terminology
-
-- [Common terminology](./prebuilt_rules_common_info.md#common-terminology).
-- **Rule source**, or **`ruleSource`**: a rule field that defines the rule's origin. Can be `internal` or `external`. Currently, custom rules have `internal` rule source and prebuilt rules have `external` rule source.
-- **`is_customized`**: a field within `ruleSource` that exists when rule source is set to `external`. It is a boolean value based on if the rule has been changed from its base version.
-- **non-semantic change**: a change to a rule field that is functionally different. We normalize certain fields so for a time-related field such as `from`, `1m` vs `60s` are treated as the same value. We also trim leading and trailing whitespace for query fields.
-
-### Assumptions
-
-- [Common assumptions](./prebuilt_rules_common_info.md#common-assumptions).
-- Rule package used will have all previous rule versions present (no missing base versions)
-
-### Non-functional requirements
-
-- [Common non-functional requirements](./prebuilt_rules_common_info.md#common-non-functional-requirements).
-
 ## Scenarios
 
 ### Editing prebuilt rules

x-pack/solutions/security/plugins/security_solution/docs/testing/test_plans/detection_response/prebuilt_rules/prebuilt_rule_export.md

@@ -2,6 +2,9 @@
 
 **Status**: `in progress`, matches [Milestone 3](https://github.com/elastic/kibana/issues/174168).
 
+> [!TIP]
+> If you're new to prebuilt rules, get started [here](./prebuilt_rules.md) and check an overview of the features of prebuilt rules in [this section](./prebuilt_rules_common_info.md#features).
+
 ## Summary <!-- omit from toc -->
 
 This is a test plan for the workflows of:
@@ -25,10 +28,11 @@ https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one
 
 - [Useful information](#useful-information)
   - [Tickets](#tickets)
-  - [User stories](#user-stories)
   - [Terminology](#terminology)
+- [Requirements](#requirements)
   - [Assumptions](#assumptions)
-  - [Non-functional requirements](#non-functional-requirements)
+  - [Technical requirements](#technical-requirements)
+  - [Product requirements](#product-requirements)
 - [Scenarios](#scenarios)
   - [Core Functionality](#core-functionality)
     - [Scenario: Exporting prebuilt rule individually from rule details page](#scenario-exporting-prebuilt-rule-individually-from-rule-details-page)
@@ -52,28 +56,38 @@ https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one
 - [Support exporting prebuilt rules from the Rule Details page](https://github.com/elastic/kibana/issues/180176)
 - [Tests for prebuilt rule import/export workflow](https://github.com/elastic/kibana/issues/202079)
 
-### User stories
-
-**Prebuilt rule export workflow:**
-
-- User can export a single prebuilt rule from the Rule Details page.
-- User can export multiple prebuilt rules one-by-one from the Rule Management page.
-- User can export multiple prebuilt rules in bulk from the Rule Management page via bulk actions.
-- User can export prebuilt non-customized rules.
-- User can export prebuilt customized rules.
-- User can export any combination of prebuilt non-customized, prebuilt customized, and custom rules.
-
 ### Terminology
 
 - [Common terminology](./prebuilt_rules_common_info.md#common-terminology).
 
+## Requirements
+
 ### Assumptions
 
+Assumptions about test environments and scenarios outlined in this test plan.
+
 - [Common assumptions](./prebuilt_rules_common_info.md#common-assumptions).
 
-### Non-functional requirements
+### Technical requirements
 
-- [Common non-functional requirements](./prebuilt_rules_common_info.md#common-non-functional-requirements).
+Non-functional requirements for the functionality outlined in this test plan.
+
+- [Common technical requirements](./prebuilt_rules_common_info.md#common-technical-requirements).
+
+### Product requirements
+
+Functional requirements for the functionality outlined in this test plan.
+
+- [Common product requirements](./prebuilt_rules_common_info.md#common-product-requirements).
+
+User stories:
+
+- User can export a single prebuilt rule from the Rule Details page.
+- User can export multiple prebuilt rules one-by-one from the Rule Management page.
+- User can export multiple prebuilt rules in bulk from the Rule Management page via bulk actions.
+- User can export prebuilt non-customized rules.
+- User can export prebuilt customized rules.
+- User can export any combination of prebuilt non-customized, prebuilt customized, and custom rules.
 
 ## Scenarios