Fix plot_pareto

[YamLyubov]

plot_pareto was using ApiParams.metric_to_compose attribute which was not set anywere. Now metric names are obtained from api_composer.

This solution might be refactored after closing #1038

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.78%. Comparing base (df1e56c) to head (9797935).
Report is 139 commits behind head on master.

Files with missing lines	Patch %	Lines
fedot/api/api_utils/params.py	0.00%	1 Missing ⚠️
fedot/api/main.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1023      +/-   ##
==========================================
- Coverage   87.80%   87.78%   -0.02%     
==========================================
  Files         208      208              
  Lines       13968    13970       +2     
==========================================
  Hits        12264    12264              
- Misses       1704     1706       +2     

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