Add support for importing delayed participations

[Virv12]

This PR adds support in cmsImportContest to import users with delayed start.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 54.66%. Comparing base (7e94024) to head (27a9f7b).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cmscontrib/ImportContest.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1609      +/-   ##
==========================================
- Coverage   54.66%   54.66%   -0.01%     
==========================================
  Files         335      335              
  Lines       27358    27360       +2     
==========================================
  Hits        14956    14956              
- Misses      12402    12404       +2     

Flag	Coverage Δ
functionaltests	0.00% <0.00%> (ø)
unittests	54.66% <50.00%> (-0.01%)	⬇️

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