[Backport 2.x] Fix bug where admin can read system index

[opensearch-trigger-bot]

Backport 5cb4dd2 from #4774.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 65.42%. Comparing base (e253e24) to head (c4d6309).
Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...rity/configuration/SystemIndexSearcherWrapper.java	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.x    #4775      +/-   ##
==========================================
- Coverage   65.46%   65.42%   -0.04%     
==========================================
  Files         319      319              
  Lines       22251    22252       +1     
  Branches     3592     3594       +2     
==========================================
- Hits        14567    14559       -8     
- Misses       5882     5889       +7     
- Partials     1802     1804       +2     

Files with missing lines	Coverage Δ
...figuration/SecurityFlsDlsIndexSearcherWrapper.java	91.66% <ø> (ø)
...rity/configuration/SystemIndexSearcherWrapper.java	91.37% <33.33%> (ø)

... and 4 files with indirect coverage changes