Add incr logging step to rails config

What does this MR do?

In response to issues encountered during a customer upgrade, the suggestion was made to highlight the requirement to enable incremental logging if an NFS share isn't used to share job log temporary files between rails nodes, in the Configure GitLab Rails sections of the reference architecture docs.

This MR adds a step to each multi-node reference architecture doc linking to the incremental logging section.

Related issues

Confidential issue

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

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Reviewer's checklist

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• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
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  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
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