Backport of docs: add plan for node rejected details and more into release/1.2.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #12564 to be assessed for backporting due to the inclusion of the label backport/1.2.x.

The below text is copied from the body of the original PR.

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• Moved federation docs to the bottom since everyone is potentially
  affected by the other sections on the page, but only users of
  federation are affected by it.
• Added section on the plan for node rejected bug since it is fairly
  easy to diagnose and removing affected nodes is a fairly reliable
  workaround.
• Mention 5s cliff for wait_for_index.
• Remove the lie that we do not have job status metrics! How old was
  that?!
• Reinforce the importance of monitoring basic system resources

[github-actions]

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