[9.1](backport #5374) [docs] Add Markdown release notes

[mergify]

🍷 Pairs with elastic/elastic-agent-changelog-tool#213 elastic/elastic-agent#9440

What is the problem this PR solves?

Currently the Elastic Agent Control Plane team generates release notes in AsciiDoc in this repo and the @elastic/ingest-docs team has to manually translate AsciiDoc to Markdown, copy to another repo (docs-content), split into multiple files, and integrate with Elastic Agent release notes. This is time consuming for the docs team and often leads to delays in publishing release notes.

How does this PR solve the problem?

In elastic/elastic-agent-changelog-tool#213, I updated the automation to allow generating Markdown, formatting it, and putting it into the correct files directly using elastic-agent-changelog-tool. This is the fleet-server output when generating the release notes using the colleenmcginnis:markdown branch of elastic-agent-changelog-tool.

This PR adds generated Markdown Fleet Server release notes here instead in the docs-content repo.

How to test this PR locally

This repo is not currently hooked up to the docs build system so we don't have a PR preview yet, but you can build the docs locally.

Note: Right now it will build independently from the rest of the Release notes, but once this repo is hooked up to the docs build system, these release notes will be integrated into the larger Release notes table of contents.

Design Checklist

This is a docs-only change.

Checklist

This is a docs-only change.

Related issues

• Update release notes for the Markdown era elastic-agent-changelog-tool#213
• [docs] Add Markdown release notes elastic-agent#9440
• https://github.com/elastic/ingest-dev/issues/5206
• https://github.com/elastic/docs-projects/issues/488

cc @ebeahan @pierrehilbert @bmorelli25

---

This is an automatic backport of pull request #5374 done by Mergify.

[mergify]

Cherry-pick of b73980b has failed:

On branch mergify/bp/9.1/pr-5374
Your branch is up to date with 'origin/9.1'.

You are currently cherry-picking commit b73980b.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   changelog/9.0.1.yaml
	new file:   changelog/9.0.2.yaml
	new file:   changelog/9.0.3.yaml
	new file:   changelog/9.0.4.yaml
	new file:   changelog/9.0.5.yaml
	new file:   changelog/9.0.6.yaml
	new file:   changelog/9.1.2.yaml
	new file:   config.changelog.yaml
	new file:   docs/release-notes/_snippets/9.0.0/breaking.md
	new file:   docs/release-notes/_snippets/9.0.0/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.0/index.md
	new file:   docs/release-notes/_snippets/9.0.1/breaking.md
	new file:   docs/release-notes/_snippets/9.0.1/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.1/index.md
	new file:   docs/release-notes/_snippets/9.0.2/breaking.md
	new file:   docs/release-notes/_snippets/9.0.2/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.2/index.md
	new file:   docs/release-notes/_snippets/9.0.3/breaking.md
	new file:   docs/release-notes/_snippets/9.0.3/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.3/index.md
	new file:   docs/release-notes/_snippets/9.0.4/breaking.md
	new file:   docs/release-notes/_snippets/9.0.4/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.4/index.md
	new file:   docs/release-notes/_snippets/9.0.5/breaking.md
	new file:   docs/release-notes/_snippets/9.0.5/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.5/index.md
	new file:   docs/release-notes/_snippets/9.0.6/breaking.md
	new file:   docs/release-notes/_snippets/9.0.6/deprecations.md
	new file:   docs/release-notes/_snippets/9.0.6/index.md
	new file:   docs/release-notes/_snippets/9.1.0/breaking.md
	new file:   docs/release-notes/_snippets/9.1.0/deprecations.md
	new file:   docs/release-notes/_snippets/9.1.0/index.md
	new file:   docs/release-notes/_snippets/9.1.1/breaking.md
	new file:   docs/release-notes/_snippets/9.1.1/deprecations.md
	new file:   docs/release-notes/_snippets/9.1.1/index.md
	new file:   docs/release-notes/_snippets/9.1.2/breaking.md
	new file:   docs/release-notes/_snippets/9.1.2/deprecations.md
	new file:   docs/release-notes/_snippets/9.1.2/index.md
	new file:   docs/release-notes/_snippets/9.1.3/breaking.md
	new file:   docs/release-notes/_snippets/9.1.3/deprecations.md
	new file:   docs/release-notes/_snippets/9.1.3/index.md
	new file:   docs/release-notes/_snippets/breaking-changes.md
	new file:   docs/release-notes/_snippets/deprecations.md
	new file:   docs/release-notes/_snippets/index.md
	new file:   docs/release-notes/breaking-changes.md
	new file:   docs/release-notes/deprecations.md
	new file:   docs/release-notes/known-issues.md

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/docset.yml
	deleted by us:   docs/release-notes/index.md
	deleted by us:   docs/release-notes/toc.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[prodsecmachine]

🎉 Snyk checks have passed. No issues have been found so far.

✅ security/snyk check is complete. No issues have been found. (View Details)

✅ license/snyk check is complete. No issues have been found. (View Details)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[karenzone]

Backporting to 9.1 to support our release notes process