Updated the get_policy API in the index_management plugin

[saimedhi]

Description

Updated the get_policy API in the index_management plugin to allow the policy_id argument as optional

Issues Resolved

Closes #629

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (c4e53d4) 72.12% compared to head (783869d) 72.14%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #633 +/- ## ========================================== + Coverage 72.12% 72.14% +0.02% ========================================== Files 89 89 Lines 7939 7935 -4 ========================================== - Hits 5726 5725 -1 + Misses 2213 2210 -3 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[dblock]

Can we add a test for this?

[saimedhi]

@saimedhi Is it not possible to generate the plugin endpoints instead of manually fixing them?

Yes @VachaShah, we need specifications and a few modifications to the generator to generate plugins in the plugins folder.