Allow to change repo user

[anbraten]

• expose repo.user_id
• allow to change repo user if not yourself
• polish UI

I've checked if we could show the user with name and its avatar instead of the user_id, but that would require quite some api adjustments (either access to the user api which seems like a bad idea or by adding the user as a part of the repo which would bloat the repo object and would be 99% of the time not used)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 21.84%. Comparing base (2f0684f) to head (e53b822).
⚠️ Report is 34 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5931      +/-   ##
==========================================
- Coverage   21.85%   21.84%   -0.02%     
==========================================
  Files         429      429              
  Lines       38821    38821              
==========================================
- Hits         8484     8479       -5     
- Misses      29560    29565       +5     
  Partials      777      777              

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