[DOCS] Add changelog configuration file

[lcawl]

Relates to elastic/docs-builder#2350

Summary

This PR adds a changelog configuration file, which contains things like the label to area mappings that will affect the creation of release notes per https://docs-v3-preview.elastic.dev/elastic/docs-builder/tree/main/contribute/changelog

The label mappings were derived from:

• https://github.com/elastic/kibana-release-notes/blob/main/src/config/templates/common.ts
• https://github.com/elastic/kibana-release-notes/blob/b97976bb42423c7b131b5a73e1ce40e4d90dcc0d/src/config/templates/kibana.ts#L6

Examples

To test the use of this configuration file:

1. Install docs-builder.

2. Run the docs-builder changelog add command to generate changelogs for a PR that uses the type and area labels that are included in the changelog.yml. For example:

   docs-builder changelog add --pr https://github.com/elastic/kibana/pull/247465  \
     --products "kibana 9.3.0" \
     --config ./kibana/docs/changelog.yml \
     --output ./kibana/docs/changelog

3. Check out Add PR label blockers to changelog creation docs-builder#2350 then refresh the docs-builder binaries per the readme:

   ./build.sh clean
   ./build.sh publishbinaries

4. Uncomment the add_blockers section of the changelog.yml file.

5. Run the docs-builder changelog add command to generate changelogs for one or more pull requests. For example, from the .artifacts/publish/docs-builder/release in the docs-builder repo:

   ./docs-builder changelog add --prs 247707,247465,246788  --repo kibana --owner elastic --products "kibana 9.3.0" --config ~/path/to/kibana/docs/changelog.yml --output ~/path/to/kibana/docs/changelog

   Re-comment the add_blockers section (unless that PR gets merged).

6. Checkout Add changelog bundle and render commands docs-builder#2341 then refresh the docs-builder binaries (per earlier step).

7. Uncomment the render_blockers section of the changelog.yml file.

8. Run the docs-builder changelog bundle and docs-builder changelog render commands to generate docs that heed the render_blockers config. For example, from the .artifacts/publish/docs-builder/release in the docs-builder repo:

   ./docs-builder changelog bundle --directory ~/path/to/kibana/docs/changelog --all
   ./docs-builder changelog render --input ~/path/to/kibana/docs/changelog/changelog-bundle.yaml --output ~/path/to/kibana/docs/release-notes/_snippets

[elasticmachine]

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