[8.4] Manual prebuilt rule updates support notice (backport #4934)

[mergify]

Resolves #3622 by adding a note explaining how automatic updates for prebuilt rule are supported per Stack version.

Previews

• Upgrade Elastic Security — New subsection
• Install and manage Elastic prebuilt rules — Add new Note

Serverless docs

No serverless docs needed, since it's versionless and always on the latest version.

Backports

Backport this all the way back. At some point the Mergify backports will fail because we reorganized both pages; use the backport tool or manually open PRs for the rest.

---

This is an automatic backport of pull request #4934 done by Mergify.

[mergify]

Cherry-pick of 9ad5d70 has failed:

On branch mergify/bp/8.4/pr-4934
Your branch is up to date with 'origin/8.4'.

You are currently cherry-picking commit 9ad5d705.
  (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)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/detections/prebuilt-rules-management.asciidoc
	both modified:   docs/upgrade/upgrade-security.asciidoc

no changes added to commit (use "git add" and/or "git commit -a")

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

[github-actions]

A documentation preview will be available soon.

• 🔨 Buildkite builds
• 📚 HTML diff
• 📙 Preview page

Request a new doc build by commenting

• Rebuild this PR: run docs-build
• Rebuild this PR and all Elastic docs: run docs-build rebuild

_{run docs-build is much faster than run docs-build rebuild. A rebuild should only be needed in rare situations.}

_{If your PR continues to fail for an unknown reason, the doc build pipeline may be broken. Elastic employees can check the pipeline status here.}