[8.17] [8.17] Document impact of using logsDB for security users (backport #6272)

[mergify]

Finishes addressing #5864 by providing 8.17 docs. Also updates the Serverless docs so they have the correct casing for logsdb.

NOTE: The content in this PR is mostly identical to the Serverless docs, save a few tweaks that change Serverless references to ESS.

Previews:

• Detection engine overview | Using logsDB index mode: Added a new section to the end of the page that directs users towards the new page that'd dedicated to explaining how rules and alerts are impacted when logsDB is enabled.
• Using logsDB index mode with Elastic Security: New page

  ---

  This is an automatic backport of pull request [8.17] Document impact of using logsDB for security users #6272 done by Mergify.

[mergify]

Cherry-pick of 61b1f1b has failed:

On branch mergify/bp/8.17/pr-6272
Your branch is up to date with 'origin/8.17'.

You are currently cherry-picking commit 61b1f1b1.
  (fix conflicts and run "git cherry-pick --continue")
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   docs/detections/detection-engine-intro.asciidoc
	modified:   docs/detections/detections-index.asciidoc
	new file:   docs/detections/detections-logsdb-impact.asciidoc

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/serverless/rules/detection-engine-overview.asciidoc
	deleted by us:   docs/serverless/rules/detections-logsdb-impact.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

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