[8.4] New page about allowlisting Elastic Endpoint in 3rd-party AV software (backport #4439)

[mergify]

This is an automatic backport of pull request #4439 done by Mergify.
Cherry-pick of 08a7c08 has failed:

On branch mergify/bp/8.4/pr-4439
Your branch is up to date with 'origin/8.4'.

You are currently cherry-picking commit 08a7c08a.
  (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:   docs/management/admin/allowlist-endpoint-3rd-party-av.asciidoc

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

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

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