[ci] Add new docs-builder automation.

[Mpdreamz]

This will enable

PR checks

• docs build successfully.
• All links from the docs to other docs are valid
• All links from other documentation to this documentation set are valid
  (e.g if we delete documentation make sure we don't break others)
• Preview builds to https://docs-v3-preview.elastic.dev/elastic/detection-rules/pull/{PR}/

• Previews clean up after a PR is closed/merged.

When merging to main we run on main to collect and publish all links to the link registry.

cc @elastic/docs-engineering

[github-actions]

Enhancement - Guidelines

These guidelines serve as a reminder set of considerations when addressing adding a feature to the code.

Documentation and Context

• Describe the feature enhancement in detail (alternative solutions, description of the solution, etc.) if not already documented in an issue.
• Include additional context or screenshots.
• Ensure the enhancement includes necessary updates to the documentation and versioning.

Code Standards and Practices

• Code follows established design patterns within the repo and avoids duplication.
• Code changes do not introduce new warnings or errors.
• Variables and functions are well-named and descriptive.
• Any unnecessary / commented-out code is removed.
• Ensure that the code is modular and reusable where applicable.
• Check for proper exception handling and messaging.

Testing

• New unit tests have been added to cover the enhancement.
• Existing unit tests have been updated to reflect the changes.
• Provide evidence of testing and validating the enhancement (e.g., test logs, screenshots).
• Validate that any rules affected by the enhancement are correctly updated.
• Ensure that performance is not negatively impacted by the changes.
• Verify that any release artifacts are properly generated and tested.

Additional Checks

• Ensure that the enhancement does not break existing functionality.
• Review the enhancement with a peer or team member for additional insights.
• Verify that the enhancement works across all relevant environments (e.g., different OS versions).
• Confirm that all dependencies are up-to-date and compatible with the changes.
• Confirm that the proper version label is applied to the PR patch, minor, major.