[DOCS] Elastic Agent release note test

[lcawl]

What does this PR do?

This PR is a test of the docs-builder changelog add and bundle commands, which are documented in https://docs-v3-preview.elastic.dev/elastic/docs-builder/tree/main/contribute/changelog

NOTE:

• The changelogs with the new format are put in a "new" sub-folder for the purposes of this test but that's not an indication of where they'll be stored in the long-term.
• I re-generated the changelogs with Fix and enhance changelog add command filename options docs-builder#2837 checked out.

Procedure

This content was created by following these steps:

1. Create a list of PRs for which we'll derive some changelogs. In this case, I grabbed it from the existing 9.3.0.yaml file.
2. Create changelogs in the new format. For example:

     docs-builder changelog add \
     --products "elastic-agent 9.3.0" \
     --config ./docs/changelog.yml --output ./changelog/new/ \
     --strip-title-prefix --use-pr-number \
     --prs ./changelog/elastic-agent-9.3.0.txt 

   NOTE: This command returns 22 errors like this:

   Error: Cannot derive type from PR https://github.com/elastic/elastic-agent/pull/11740 labels (Team:Elastic-Agent-Control-Plane, backport-9.3). No matching label found in type mapping. Please provide --type or add pivot.types with labels in changelog.yml.

   This is due to the lack "type" labels on the problematic PRs.
3. To work around the missing type labels temporarily, we could create them one-by-one with commands like this, but the long-term solution is to ensure there are "type" labels on every PR:

   docs-builder changelog add \
   --products "elastic-agent 9.3.0" \
   --config ./docs/changelog.yml --output ./changelog/new/ \
   --strip-title-prefix --use-pr-number \
   --prs https://github.com/elastic/elastic-agent/pull/11418 \
   --type feature
   
   docs-builder changelog add \
   --products "elastic-agent 9.3.0" \
   --config ./docs/changelog.yml --output ./changelog/new/ \
   --strip-title-prefix --use-pr-number \
   --prs https://github.com/elastic/elastic-agent/pull/12187 \
   --type breaking-change
   
   docs-builder changelog add \
   --products "elastic-agent 9.3.0" \
   --config ./docs/changelog.yml --output ./changelog/new/ \
   --strip-title-prefix --use-pr-number \
   --prs https://github.com/elastic/elastic-agent/pull/9363 \
   --type feature

   NOTE: This last command fails with the following message:

   Warning: Skipping changelog creation for PR https://github.com/elastic/elastic-agent/pull/9363 due to global blocking label 'skip-changelog'. This label is configured to prevent changelog creation.

   This is proof that the block.create section of the changelog.yml configuration file is working.
4. Create a bundle of all the changelogs. This can be done based on a PR list, the changelog product metadata, or all changelogs in a folder. For example, to simply bundle everything in the directory:

        docs-builder changelog bundle \
      --directory ./changelog/new \
      --output ./docs/changelog/bundles/9.3.0.yaml \
      --all --resolve

   Alternatively, to bundle based on PR list:

   docs-builder changelog bundle \
     --directory ./changelog/new \
     --output ./docs/changelog/bundles/9.3.0.yaml \
     --prs ./changelog/elastic-agent-9.3.0.txt \
     --resolve

   In this case, there will be warnings about the missing changelogs, since we didn't address all the PRs with missing type labels.
   Alternatively, use a profile to create the bundle based on the PR list (requires Changelog profile parity - final phases docs-builder#2808):

   docs-builder/release/docs-builder changelog bundle elastic-agent-release 9.3.0 ./changelog/elastic-agent-9.3.0.txt

5. Add the changelog directives so that all future bundles in this format will be automatically published.
6. Alternatively, it's possible to render the bundle as markdown snippets each time there's a release, for example:

   docs-builder changelog render \
     --config ./docs/changelog.yml \
     --input "/path/to/elastic-agent/docs/changelog/bundles/9.3.0.yaml|/path/to/elastic-agent/changelog/new|elastic-agent|keep-links" \
     --output ./docs/release-notes/_snippets/

   You must then add references to these snippets in the existing release note docs. Since this requires effort every release, it's not the recommended option.

Why is it important?

These new tools and changelog formats are intended to eventually be used in a consistent manner across all repos.

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
  - [ ] I have added tests that prove my fix is effective or that my feature works
  - [ ] I have added an entry in ./changelog/fragments using the changelog tool
  - [ ] I have added an integration test or an E2E test

Disruptive User Impact

No, this is for testing purposes only

How to test this PR locally

To preview the output locally:

1. Install docs-builder (https://www.elastic.co/docs/contribute-docs/locally#install-docs-builder)
2. Launch the preview: docs-builder serve -p /path/to/elastic-agent/docs

For example:

Related issues

Relates https://github.com/elastic/docs-content-internal/issues/188

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b rn-test upstream/rn-test
git merge upstream/9.3
git push upstream rn-test

[github-actions]

🔍 Preview links for changed docs

• docs/release-notes/breaking-changes.md
• docs/release-notes/deprecations.md
• docs/release-notes/index.md
• docs/release-notes/known-issues.md

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b rn-test upstream/rn-test
git merge upstream/9.3
git push upstream rn-test

[github-actions]

✅ Vale Linting Results

No issues found on modified lines!

---

The Vale linter checks documentation changes against the Elastic Docs style guide.

To use Vale locally or report issues, refer to Elastic style guide for Vale.