Optimize DB requests

[zhiltsov-max]

Motivation and context

Optimizes several DB request memory issues, introduced in #6204

• Optimized memory use in job annotation retrieval
• Optimized migration

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added a description of my changes into the CHANGELOG file
• 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 #6340 (1b2e8db) into develop (9db68a3) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop    #6340      +/-   ##
===========================================
- Coverage    79.76%   79.76%   -0.01%     
===========================================
  Files          321      321              
  Lines        37323    37329       +6     
  Branches      6753     6756       +3     
===========================================
+ Hits         29772    29774       +2     
- Misses        7283     7287       +4     
  Partials       268      268              

Components	Coverage Δ
cvat-ui	77.11% <ø> (-0.02%)	⬇️
cvat-server	82.15% <66.66%> (+<0.01%)	⬆️

[azhavoro]

@zhiltsov-max Could you add a note to the changelog please?