RCAL-568: remove ModelContainer from datamodels.

[mairanteodoro]

Resolves RCAL-568

This PR removes ModelContainer from roman_datamodels.datamodels.

Checklist

• Added entry in CHANGES.rst under the corresponding subsection
• updated relevant tests
• updated relevant documentation
• Passed romancal regression testing on Jenkins / PLWishMaster. Link: https://plwishmaster.stsci.edu:8081/job/RT/job/romancal/XXX/

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.15 🎉

Comparison is base (562040a) 97.89% compared to head (38f911c) 98.05%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #204      +/-   ##
==========================================
+ Coverage   97.89%   98.05%   +0.15%     
==========================================
  Files           8        8              
  Lines        1285     1234      -51     
==========================================
- Hits         1258     1210      -48     
+ Misses         27       24       -3     

Impacted Files	Coverage Δ
tests/test_models.py	98.64% <100.00%> (+0.40%)	⬆️

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[PaulHuwe]

LGTM