make train data optional on RAIBaseInsights class

[imatiach-msft]

Description

Make train data optional on RAIBaseInsights class.
The train data is optional for RAITextInsights and RAIVisionInsights as it is not used currently.

Checklist

• I have added screenshots above for all UI changes.
• I have added e2e tests for all UI changes.
• Documentation was updated if it was needed.

[codecov-commenter]

Codecov Report

Merging #2029 (35fd614) into main (7a56868) will decrease coverage by 0.02%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##             main    #2029      +/-   ##
==========================================
- Coverage   92.32%   92.31%   -0.02%     
==========================================
  Files          95       95              
  Lines        4902     4908       +6     
==========================================
+ Hits         4526     4531       +5     
- Misses        376      377       +1     

Flag	Coverage Δ
unittests	92.31% <92.85%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
...ai/responsibleai/rai_insights/rai_base_insights.py	86.09% <92.85%> (-0.12%)	⬇️

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[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/ilmat/optional-train-insights/dashboard/index.html

[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/ilmat/optional-train-insights/dashboard/index.html