Change _opendistro/_security/saml/acs to /_plugins/_security/saml/acs

[kzinas-adv]

Description

Change _opendistro/_security/saml/acs to /_plugins/_security/saml/acs

• Category (Bug fix, Test fix, Refactoring, Maintenance)
• Why these changes are required?
  Project opensearch-project/security-dashboards-plugin in version 2.1.0 changed SAML2 authentication endpoint to _plugins/_security/saml/acs while opensearch-project/security use old /_opendistro/_security/saml/acs
  This creates clash as users need modify this place by hand to get SAML working.
• What is the old behavior before changes and new behavior after changes?
  Before this change users will need to change endpoint by hand back to _opendistro/ in /usr/share/opensearch-dashboards/plugins/securityDashboards/server/auth/types/saml/routes.js after installing or upgrading to opensearch-dashboards.

Issues Resolved

[List any issues this PR will resolve]
#1941

Testing

I just build recent security project and used it with opensearch 2.1.0 using SAML with /_plugins/ endpoint and it worked .

Check List

• New functionality includes testing
• New functionality has been documented
• 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.

[peternied]

Thanks for this pull request, we can merge this against the 3.0.0 version of the plugin, to merge this we do need the DCO signoff on each commit and an integration test.

A note for our future 2.1.X/2.2.0 releases we would need a backward compatible version of this change - how do you feel about making those modifications?

[codecov-commenter]

Codecov Report

Merging #1949 (bb56f61) into main (f153c27) will not change coverage.
The diff coverage is 50.00%.

@@            Coverage Diff            @@
##               main    #1949   +/-   ##
=========================================
  Coverage     61.01%   61.01%           
+ Complexity     3235     3234    -1     
=========================================
  Files           256      256           
  Lines         18088    18088           
  Branches       3224     3224           
=========================================
  Hits          11036    11036           
- Misses         5468     5470    +2     
+ Partials       1584     1582    -2     

Impacted Files	Coverage Δ
...zon/dlic/auth/http/saml/Saml2SettingsProvider.java	61.53% <50.00%> (ø)
...iance/ComplianceIndexingOperationListenerImpl.java	60.86% <0.00%> (-1.45%)	⬇️
...a/org/opensearch/security/tools/SecurityAdmin.java	37.31% <0.00%> (-0.25%)	⬇️
...search/security/transport/SecurityInterceptor.java	76.15% <0.00%> (+0.76%)	⬆️
...security/auditlog/sink/ExternalOpenSearchSink.java	61.72% <0.00%> (+2.46%)	⬆️

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[kzinas-adv]

Same changes went much further https://github.com/opensearch-project/security/pull/1936/commits