RAIInsights: prevent failures on optional methods & fix feature range formatting for timestamps

[romanlutz]

Description

With optional methods such as forecast_quantiles we need to be able to check if the model has the method at all without getting a failure. This PR adjusts the handling slightly to prevent unintended issues.

Secondly, the feature ranges need to be specified in a JSON-serializable format, so we're storing them as strings now.

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 #2258 (b7f5af3) into main (51a2982) will increase coverage by 0.84%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main    #2258      +/-   ##
==========================================
+ Coverage   92.26%   93.10%   +0.84%     
==========================================
  Files         103      103              
  Lines        5171     5179       +8     
==========================================
+ Hits         4771     4822      +51     
+ Misses        400      357      -43     

Flag	Coverage Δ
unittests	93.10% <80.00%> (+0.84%)	⬆️

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

Files Changed	Coverage Δ
...sibleai/responsibleai/rai_insights/rai_insights.py	90.36% <80.00%> (+2.62%)	⬆️

... and 1 file with indirect coverage changes

[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/romanlutz/rai_insights_fix/dashboard/index.html

[gaugup]

Could add unit tests for these changes?

[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/romanlutz/rai_insights_fix/dashboard/index.html

[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/romanlutz/rai_insights_fix/dashboard/index.html

[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/romanlutz/rai_insights_fix/dashboard/index.html

[romanlutz]

Could add unit tests for these changes?

Added tests as requested.