Add email service

[ttoino]

Closes #82.

Adds a new EmailService with a method send, which receives an instance of EmailBuilder.
Two builders were implemented: SimpleEmailBuilder, which receives all properties directly, and TemplateEmailBuilder, which generates the subject, content and attachments from the given data using mustache templates.

Each different template email should be a subclass of TemplateEmailBuilder, here's an example:

data class ExampleContext(
    val title: String,
    val todos: List<String>
)

class ExampleEmailBuilder : TemplateEmailBuilder<ExampleContext>("example")

<!-- .../resources/templates/email/example.mustache -->
---
subject: Example: {{title}}
attachments:
    - {{title}}.txt :: classpath:application.properties
inline:
    - image :: classpath:image.png
---

# {{title}}

{{#todos}}
- {{.}}
{{/todos}}

![Image](cid:image)

service.send(
    ExampleEmailBuilder()
        .data(ExampleContext("Grocery list", listOf("Potatoes", "Tomatoes", "Cheese")))
        .to("email@email.com")
)

This sends an email that looks something like this:

Review checklist

• Contains enough appropriate tests
• Behavior is as expected
• Clean, well structured code

[codecov-commenter]

Codecov Report

Patch coverage: 16.66% and project coverage change: -11.07 ⚠️

Comparison is base (2a423b6) 88.49% compared to head (33dc731) 77.43%.

Additional details and impacted files

@@              Coverage Diff               @@
##             develop     #123       +/-   ##
==============================================
- Coverage      88.49%   77.43%   -11.07%     
- Complexity       345      355       +10     
==============================================
  Files             61       67        +6     
  Lines            791      935      +144     
  Branches          65       76       +11     
==============================================
+ Hits             700      724       +24     
- Misses            57      177      +120     
  Partials          34       34               

Impacted Files	Coverage Δ
.../pt/up/fe/ni/website/backend/BackendApplication.kt	50.00% <ø> (ø)
...up/fe/ni/website/backend/email/BaseEmailBuilder.kt	0.00% <0.00%> (ø)
.../fe/ni/website/backend/email/SimpleEmailBuilder.kt	0.00% <0.00%> (ø)
...e/ni/website/backend/email/TemplateEmailBuilder.kt	0.00% <0.00%> (ø)
...t/up/fe/ni/website/backend/service/EmailService.kt	37.50% <37.50%> (ø)
.../fe/ni/website/backend/config/email/EmailConfig.kt	100.00% <100.00%> (ø)
...site/backend/config/email/EmailConfigProperties.kt	100.00% <100.00%> (ø)

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[ttoino]

I'm marking as ready for review, but a few things are still missing:

• Support for images and other embedded resources like styles
• Default email layout and styles - Supported, design not finalized
• Some kind of testing (not sure what to do here)
• Maybe markdown support
• Documentation - in the wiki

[github-actions]

Check the documentation preview: https://64148c8507396b40a734ad10--niaefeup-backend-docs.netlify.app

[github-actions]

Check the documentation preview: https://64161557a5113f2455baeb87--niaefeup-backend-docs.netlify.app

[BrunoRosendo]

What a great PR 🎉 Tremendous job! I left minor/cosmetic suggestions

One thing I don't like is having email as a top-level package, I think we already have enough of them. What do you think of storing the builders under service/email/? together with EmailService?

[BrunoRosendo]

this function is a bit verbose, I'd consider splitting it into more methods if possible

[github-actions]

Check the documentation preview: https://641c7e9b8ddee704dad18da7--niaefeup-backend-docs.netlify.app

[BrunoRosendo]

Have you decided something about the tests?

[github-actions]

Check the documentation preview: https://649c5a2becd22626c57b25e2--niaefeup-backend-docs.netlify.app

[github-actions]

Check the documentation preview: https://6748a29cc73b7330bd8b3797--niaefeup-backend-docs.netlify.app

[github-actions]

Check the documentation preview: https://6793cddd62e627d5c653cc1b--niaefeup-backend-docs.netlify.app

[MRita443]

It's looking good so far. Shouldn't we add tests for SimpleEmailBuilder and TemplateEmailBuildertoo?

[rubuy-74]

Don't forget to add instructions for testing on the wiki.

[BrunoRosendo]

I like the changes from the last time I saw it. Good job with the tests!

One thing that would be great to improve is the size of the PRs. We didn't use to do this in NI but it's much easier to do small and incremental PRs, even if the feature or issue isn't fully closed. This should help make the reviews quicker and avoid having stale CRs for months at a time

PS: you need to fix the lint, it seems

[BrunoRosendo]

approve to unblock, but look at the comments

[MRita443]

Great job with the tests! There's some simple errors as of now if you could fix that. And don't forget the lint and comments here

[github-actions]

Check the documentation preview: https://67c0b65a3bf3287b25d1df13--niaefeup-backend-docs.netlify.app

[MRita443]

Great job! A comment for posteriority: If the email tests and application context load fails, delete the website-be-h2-db.mv.db file in your home folder

[github-actions]

Check the documentation preview: https://67cdae385ff4f4a51dcb8f90--niaefeup-backend-docs.netlify.app

[github-actions]

Check the documentation preview: