Fix custom sql filtering support: bring back backward compatibility

[mahenzon]

No description provided.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (0d716a4) 76.95% compared to head (c918b5f) 77.09%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
+ Coverage   76.95%   77.09%   +0.14%     
==========================================
  Files          40       40              
  Lines        2434     2449      +15     
  Branches      356      358       +2     
==========================================
+ Hits         1873     1888      +15     
- Misses        488      489       +1     
+ Partials       73       72       -1     

Flag	Coverage Δ
unittests	77.09% <80.00%> (+0.14%)	⬆️

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Files	Coverage Δ
fastapi_jsonapi/__init__.py	100.00% <100.00%> (ø)
...astapi_jsonapi/data_layers/filtering/sqlalchemy.py	83.17% <79.06%> (+1.17%)	⬆️