[BF] Auto extractors and merge regex expressions

[arnaudbore]

Before this fix, auto_extract_entities was trying to feed all entities found with auto_extractors even if auto_entities was more strict.

Also when providing custom extractors it was overwrote by auto_extractors.

Need some testing, @SamGuay I will send you some data.

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (42cd77b) 75.16% compared to head (51af3f9) 75.25%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #275      +/-   ##
==========================================
+ Coverage   75.16%   75.25%   +0.09%     
==========================================
  Files          15       15              
  Lines        1075     1079       +4     
  Branches      237      239       +2     
==========================================
+ Hits          808      812       +4     
  Misses        220      220              
  Partials       47       47              

Flag	Coverage Δ
pytest	75.25% <100.00%> (+0.09%)	⬆️

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Files	Coverage Δ
dcm2bids/sidecar.py	81.13% <100.00%> (+0.11%)	⬆️
dcm2bids/utils/utils.py	84.04% <100.00%> (+0.34%)	⬆️

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[SamGuay]

Test data were converted successfully! This bf makes it clear whats expected from the user now, I think.