[8.18] Security 8.18.8 release notes (backport #7080)

[mergify]

Resolves #7077: adds the 8.18.8 Security and Endpoint release notes.

Preview: 8.18

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This is an automatic backport of pull request #7080 done by Mergify.

[mergify]

Cherry-pick of cef7330 has failed:

On branch mergify/bp/8.18/pr-7080
Your branch is up to date with 'origin/8.18'.

You are currently cherry-picking commit cef7330f.
  (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:
	modified:   docs/release-notes/8.18.asciidoc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   docs/release-notes.asciidoc

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]

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