Add troubleshooting tips for tags not being properly deleted

What does this MR do and why?

This MR adds some steps to troubleshoot tags not being properly deleted, though the deletion requests are logged as successful.

Related issue: container-registry#551 (closed)

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

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

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.