[Backport 2.x] Adds default roles for Snapshot Management plugin

[opensearch-trigger-bot]

Backport 7f5ca53 from #1897

[codecov-commenter]

Codecov Report

Merging #1902 (7f5ca53) into 2.x (8393c71) will decrease coverage by 0.03%.
The diff coverage is n/a.

❗ Current head 7f5ca53 differs from pull request most recent head 4372537. Consider uploading reports for the commit 4372537 to get more accurate results

@@             Coverage Diff              @@
##                2.x    #1902      +/-   ##
============================================
- Coverage     61.04%   61.00%   -0.04%     
+ Complexity     3234     3232       -2     
============================================
  Files           256      256              
  Lines         18088    18088              
  Branches       3224     3224              
============================================
- Hits          11041    11035       -6     
- Misses         5467     5470       +3     
- Partials       1580     1583       +3     

Impacted Files	Coverage Δ
...urity/ssl/transport/SecuritySSLNettyTransport.java	62.36% <0.00%> (-4.31%)	⬇️
...security/auditlog/sink/ExternalOpenSearchSink.java	59.25% <0.00%> (-2.47%)	⬇️
...earch/security/ssl/util/SSLConnectionTestUtil.java	93.18% <0.00%> (-2.28%)	⬇️
...a/org/opensearch/security/tools/SecurityAdmin.java	37.56% <0.00%> (+0.24%)	⬆️

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[DarshitChanpura]

Closing this PR as merge conflicts are resolved here in a new PR: #1916