Allow disabling per group f1 scores in customF1

[yoavkatz]

Sometimes there are many groups in customF1 and it's not interesting to see results for each.

This PR allows disabling the reporting of these score.

[codecov]

Codecov Report

Attention: Patch coverage is 96.87500% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 90.87%. Comparing base (e352dd4) to head (80edc73).

Files	Patch %	Lines
src/unitxt/metrics.py	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #719      +/-   ##
==========================================
+ Coverage   90.17%   90.87%   +0.70%     
==========================================
  Files          98       98              
  Lines        9546     9569      +23     
==========================================
+ Hits         8608     8696      +88     
+ Misses        938      873      -65     

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