Add Gitaly Troubleshooting Section

What does this MR do and why?

This MR adds a troubleshooting section referencing the recent changes introduced in GitLab 15.5 on how GitLab now communicates with th GitLab Shell. JWT Tokens are now used, and customers may encounter 401 Unauthorized errors if they do not upgrade Gitaly prior to upgrading other application nodes.

Internal Support ticket for reference.

Screenshots or screen recordings

N/A

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

N/A

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.