Add backend functions in explainer_manager.py to handle dashboard requests

[gaugup]

Description

Add function request_explanations to explainer_manager.py to handle explanations requests from RAI dashboard

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 #1585 (fd1447a) into main (24ae91a) will increase coverage by 0.75%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1585      +/-   ##
==========================================
+ Coverage   88.12%   88.87%   +0.75%     
==========================================
  Files         109      109              
  Lines        5323     5332       +9     
==========================================
+ Hits         4691     4739      +48     
+ Misses        632      593      -39     

Flag	Coverage Δ
unittests	88.87% <100.00%> (+0.75%)	⬆️

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

Impacted Files	Coverage Δ
...ibleai/responsibleai/managers/explainer_manager.py	89.55% <100.00%> (+20.80%)	⬆️

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[github-actions]

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

[github-actions]

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