Add methods and constants for genai metrics

[kartikc727]

Adding all the new methods and constants for the new generative text task types.

Full support for the new task type would require more changes but this PR is meant to add all the new methods without breaking the working of any of the existing task types.

[codecov-commenter]

Codecov Report

Attention: 48 lines in your changes are missing coverage. Please review.

Comparison is base (5036435) 88.39% compared to head (874857a) 78.52%.

Files	Patch %	Lines
...ibleai_text/rai_text_insights/rai_text_insights.py	15.38%	33 Missing ⚠️
...ponsibleai_text/managers/error_analysis_manager.py	33.33%	8 Missing ⚠️
...ext/responsibleai_text/utils/feature_extractors.py	30.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2524      +/-   ##
==========================================
- Coverage   88.39%   78.52%   -9.88%     
==========================================
  Files         142       36     -106     
  Lines        7961     2598    -5363     
==========================================
- Hits         7037     2040    -4997     
+ Misses        924      558     -366     

Flag	Coverage Δ
unittests	78.52% <30.43%> (-9.88%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.