[DOCS] Add changelog config file

[lcawl]

Release notes

[rn:skip]

What does this PR do?

This PR adds a configuration file for release note changelog tooling per https://elastic.github.io/docs-builder/contribute/configure-changelogs/

Why is it important/What is the impact to the user?

This file defines when/if changelogs will be created and rules for how the changelogs will be bundled at release time.

Checklist

• 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 (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• [ ]

How to test this PR locally

Related issues

Use cases

Screenshots

Logs

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)
• run exhaustive tests : Run the exhaustive tests Buildkite pipeline.

[mergify]

This pull request does not have a backport label. Could you fix it @lcawl? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• If no backport is necessary, please add the backport-skip label

[github-actions]

🔍 Preview links for changed docs

⏳ Building and deploying preview... View progress

This comment will be updated with preview links when the build is complete.