What this PR does / why we need it:
Updates the ppl endpoint to then newer _plugins endpoint.
The _opendistro endpoint was deprecated (link) , and opensearch has supported the _plugin endpoint since 1.0.0 (link)
Which issue(s) this PR fixes:
Fixes #499
Special notes for your reviewer:
I decided not to update the frontend query code since we're planning to remove it, but I can if we think it would make sense
What this PR does / why we need it: Updates the ppl endpoint to then newer _plugins endpoint. The _opendistro endpoint was deprecated (link) , and opensearch has supported the _plugin endpoint since 1.0.0 (link)
Which issue(s) this PR fixes:
Fixes #499
Special notes for your reviewer: I decided not to update the frontend query code since we're planning to remove it, but I can if we think it would make sense