Fix GT job creation races

[zhiltsov-max]

Motivation and context

It's possible to get more than 1 GT job in a task in the case of concurrent creation requests.
This PR fixes this by introducing a task row-level lock in the DB for the update transaction.

• Fixed GT job creation race condition

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 #7096 (e9d0212) into develop (060fef0) will increase coverage by 0.08%.
Report is 10 commits behind head on develop.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #7096      +/-   ##
===========================================
+ Coverage    82.30%   82.39%   +0.08%     
===========================================
  Files          361      361              
  Lines        39222    39310      +88     
  Branches      3588     3591       +3     
===========================================
+ Hits         32283    32390     +107     
+ Misses        6939     6920      -19     

Components	Coverage Δ
cvat-ui	77.34% <ø> (+0.04%)	⬆️
cvat-server	87.02% <100.00%> (+0.11%)	⬆️

[nmanovic]

LGTM