Revert "Revert "Replace _opendistro route with _plugins""

[DarshitChanpura]

This PR brings in the original changes that were reverted due to broken SAML authentication issue.

NOTE: This PR shouldn't be merged until opensearch-project/security#1936 is merged

Related Issues:
#1031
opensearch-project/security#1941

[codecov-commenter]

Codecov Report

Merging #1038 (a506d7a) into main (cc5b763) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1038   +/-   ##
=======================================
  Coverage   72.27%   72.27%           
=======================================
  Files          87       87           
  Lines        1915     1915           
  Branches      244      244           
=======================================
  Hits         1384     1384           
  Misses        478      478           
  Partials       53       53           

[cliu123]

@DarshitChanpura Is this PR ready?

[DarshitChanpura]

@DarshitChanpura Is this PR ready?

The PR is ready but we have to wait until opensearch-project/security#1936 is merged.

[peternied]

@DarshitChanpura Lets create a fresh PR with the change we would like to see, this revert revert is a little confounding