Deprecate opendistro API paths

[shikharj05]

Description

[Describe what this change achieves]

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation) Maintenance

• Why these changes are required?
  The security repo has lingering usages of the legacy terms like _opendistro is API paths, these are replaced with _plugins prefix, however legacy paths are not explicitly marked as deprecated.

• What is the old behavior before changes and new behavior after changes?

Issues Resolved

#5097

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

TODO

Check List

• [TODO] New functionality includes testing
• [TODO] New functionality has been documented
• [NA] New Roles/Permissions have a corresponding security dashboards plugin PR
• [NA] 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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.65%. Comparing base (e1c05c3) to head (cb87420).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5102      +/-   ##
==========================================
+ Coverage   71.55%   71.65%   +0.10%     
==========================================
  Files         336      336              
  Lines       22649    22715      +66     
  Branches     3603     3603              
==========================================
+ Hits        16206    16277      +71     
  Misses       4641     4641              
+ Partials     1802     1797       -5     

Files with missing lines	Coverage Δ
.../opensearch/security/OpenSearchSecurityPlugin.java	83.79% <ø> (ø)
...earch/security/dlic/rest/api/AccountApiAction.java	98.64% <100.00%> (+0.05%)	⬆️
.../security/dlic/rest/api/ActionGroupsApiAction.java	98.27% <100.00%> (+0.09%)	⬆️
...nsearch/security/dlic/rest/api/AuditApiAction.java	91.17% <100.00%> (-2.67%)	⬇️
...curity/dlic/rest/api/AuthTokenProcessorAction.java	92.85% <100.00%> (+1.94%)	⬆️
...security/dlic/rest/api/ConfigUpgradeApiAction.java	87.41% <100.00%> (+0.25%)	⬆️
...ch/security/dlic/rest/api/FlushCacheApiAction.java	67.85% <100.00%> (+3.85%)	⬆️
...security/dlic/rest/api/InternalUsersApiAction.java	93.54% <100.00%> (+0.15%)	⬆️
...ity/dlic/rest/api/MultiTenancyConfigApiAction.java	90.90% <100.00%> (+0.36%)	⬆️
...earch/security/dlic/rest/api/NodesDnApiAction.java	90.90% <100.00%> (+1.16%)	⬆️
... and 13 more

... and 10 files with indirect coverage changes

[cwperks]

@shikharj05 The changes look good to me in this PR. What is remaining before taking it out of draft?