[8.1] Replace placeholder URLs (backport #6990)

[mergify]

Contributes to elastic/docs-content#1806.

---

This is an automatic backport of pull request #6990 done by Mergify.

[mergify]

Cherry-pick of 1633469 has failed:

On branch mergify/bp/8.1/pr-6990
Your branch is up to date with 'origin/8.1'.

You are currently cherry-picking commit 1633469.
  (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/AI-for-security/connect-to-byo.asciidoc
	deleted by us:   docs/cloud-native-security/cspm-get-started-aws.asciidoc
	deleted by us:   docs/cloud-native-security/kspm-get-started.asciidoc
	deleted by us:   docs/detections/prebuilt-rules/rule-details/multiple-vault-web-credentials-read.asciidoc
	deleted by us:   docs/release-notes/8.16.asciidoc
	deleted by us:   docs/release-notes/8.8.asciidoc
	deleted by us:   docs/release-notes/8.9.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

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[natasha-moore-elastic]

Closing as none of the updated files exist in the 8.1 branch.