Note that NFS for gitaly is deprecated

What does this MR do?

Notes that NFS for Gitaly is deprecated, and removes the recommendation for a minimum of 2 nodes.

Closes #220335 (closed)

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

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• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
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