Added user deletion manager that removes user together with all data

[bsekachev]

Motivation and context

• The manager supports validation (e.g. in community version user should not have organizations with other members, in SaaS user also should not have any active subscriptions)
• Added command: python manage.py deleteuser <user_id>

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 70 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.44%. Comparing base (eed6960) to head (36d6459).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #9686      +/-   ##
===========================================
- Coverage    80.24%   75.44%   -4.81%     
===========================================
  Files          400      457      +57     
  Lines        44437    47476    +3039     
  Branches      3974     3974              
===========================================
+ Hits         35660    35819     +159     
- Misses        8777    11657    +2880     

Components	Coverage Δ
cvat-ui	77.58% <ø> (-0.03%)	⬇️
cvat-server	73.81% <0.00%> (-8.70%)	⬇️

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud