Small refactoring

[Marishka17]

Motivation and context

This PR contains several small fixes:

• Removed API endpoint GET /api/assets/<uuid>/public. Logic for retrieving public assets moved into GET /api/assets/<uuid> endpoint
• Removed ability to set builders for iam_context because it is no longer needed
• Changed approach to assigning a group to a user

Depends on #7259

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)
• I have increased versions of npm packages if it is necessary
  (cvat-canvas,
  cvat-core,
  cvat-data and
  cvat-ui)

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]

Codecov Report

Merging #7149 (840ab9d) into develop (d9e7b2c) will decrease coverage by 0.02%.
The diff coverage is 95.08%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7149      +/-   ##
===========================================
- Coverage    83.09%   83.08%   -0.02%     
===========================================
  Files          371      372       +1     
  Lines        39532    39530       -2     
  Branches      3671     3671              
===========================================
- Hits         32850    32842       -8     
- Misses        6682     6688       +6     

Components	Coverage Δ
cvat-ui	78.68% <ø> (-0.05%)	⬇️
cvat-server	87.09% <95.08%> (+<0.01%)	⬆️