Removes unused get/post/put cache endpoint

[derek-ho]

Description

Removes Get, Post, Put cache API routes, since only delete is used. This should not be backported to 2.x, and we should add a deprecation notice there as well (although these were never used anyway so the behavior should be consistent)

Issues Resolved

[List any issues this PR will resolve]

Is this a backport? If so, please add backport PR # and/or commits #, and remove backport-failed label from the original PR.

Do these changes introduce new permission(s) to be displayed in the static dropdown on the front-end? If so, please open a draft PR in the security dashboards plugin and link the draft PR here

Testing

[Please provide details of testing done: unit testing, integration testing and manual testing]

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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.

[derek-ho]

@DarshitChanpura how do we mark this as deprecated in the 2.x line? Just add a Java annotation @ Deprecated?

[cwperks]

@derek-ho We can use the DeprecationLogger and add a warning to the API response if someone calls the endpoint with one of the deprecated verbs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.60%. Comparing base (df115d8) to head (6498e53).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4761      +/-   ##
==========================================
- Coverage   65.64%   65.60%   -0.04%     
==========================================
  Files         321      321              
  Lines       22539    22538       -1     
  Branches     3611     3611              
==========================================
- Hits        14795    14786       -9     
- Misses       5932     5939       +7     
- Partials     1812     1813       +1     

Files with missing lines	Coverage Δ
...ch/security/dlic/rest/api/FlushCacheApiAction.java	64.00% <100.00%> (-1.39%)	⬇️

... and 2 files with indirect coverage changes

[willyborankin]

@derek-ho could you please fix Code Hygiene / Spotless scan (pull_request) Failing ?

[cwperks]

@derek-ho Can you also raise a PR against the API specification repo to reflect this change?

ref: https://github.com/opensearch-project/opensearch-api-specification/blob/main/spec/namespaces/security.yaml#L449-L498

[cwperks]

Merging this into main. @derek-ho please open a backport with the deprecation messages discussed above.