Add basic docs for troubleshooting database problems

What does this MR do?

Add basic docs for troubleshooting database problems

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Not easy to find quick snippets to run when you database breaks.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Review
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?