Enhanced errors notifications

[bsekachev]

Motivation and context

Resolved #7365

Examples:

instead of

instead of

instead of

instead of

instead of

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.

[bsekachev]

Wrong exception class used, it caused 500 server error because of unhandled exception

[codecov]

Codecov Report

Merging #7371 (16a6a78) into develop (d25b863) will decrease coverage by 0.06%.
Report is 5 commits behind head on develop.
The diff coverage is 83.33%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7371      +/-   ##
===========================================
- Coverage    83.26%   83.20%   -0.06%     
===========================================
  Files          373      373              
  Lines        39615    39714      +99     
  Branches      3701     3720      +19     
===========================================
+ Hits         32984    33043      +59     
- Misses        6631     6671      +40     

Components	Coverage Δ
cvat-ui	78.93% <85.71%> (-0.11%)	⬇️
cvat-server	87.12% <50.00%> (+<0.01%)	⬆️

[klakhov]

@bsekachev
If rest_framework.exceptions.ValidationError contains just a string:
raise ValidationError("just a string rest_framework.exceptions.ValidationError")
we get a 0 key in message, which is not good: