[8.x] Spaces in serverless (backport #5813)

[mergify]

Resolves https://github.com/elastic/security-docs-internal/issues/31. Also fixes #6019.

Preview

• Click the link in the comment below, then in the Security card click View serverless docs.
• Navigate to: Elastic Security UI → Spaces and Elastic Security

Note that we're no longer trying to omit "Kibana" from serverless docs, as that no longer seems to be a requirement (it's all over the UI). So this content mostly mirrors the ESS version in sometimes referring to spaces as "KIbana spaces," though in some instances this has been shortened to just "spaces" for simplicity.

---

This is an automatic backport of pull request #5813 done by Mergify.

[mergify]

Cherry-pick of 686800d has failed:

On branch mergify/bp/8.x/pr-5813
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit 686800d3.
  (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/events/timeline-templates.asciidoc
	modified:   docs/events/timeline-ui-overview.asciidoc
	modified:   docs/getting-started/data-views-in-sec.asciidoc
	modified:   docs/getting-started/security-spaces.asciidoc
	new file:   docs/serverless/security-spaces.mdx

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/serverless/explore/data-views-in-sec.mdx
	deleted by us:   docs/serverless/investigate/timeline-templates-ui.mdx
	deleted by us:   docs/serverless/investigate/timelines-ui.mdx
	deleted by us:   docs/serverless/sec-requirements.mdx
	deleted by us:   docs/serverless/serverless-security.docnav.json

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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