Fix user membership destroy relation

What does this MR do?

Add a foreign key to Member to automatically remove rows when the user is deleted

Why was this MR needed?

Because when it might happen that there was a problem with the user removal and some records of Member could persist.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • 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?

Closes #40053 (closed)