[2.19] Quick fix for tenant privilege performance issues

[nibix]

Description

This is a minimal quick fix to solve the performance issues described in #5342 and #5129 also for OpenSearch 2.19.

It won't be as fast as the implementation in #5350, as it still requires loops. Still, micro benchmarks on ConfigModelV7.mapTenants() show a huge improvement (10 threads, 10000 iterations):

• 2.19.1 release version: 2.14 ms per call
• This change: 0.065 ms per call

This can be achieved by avoiding calls to SecurityDynamicConfiguration.getCEntries() which will always copy the config HashMap in a synchronized block - thus very strongly limiting the concurrency on the particular node.

• Category: Performance improvement
• Why these changes are required? Performance issues on clusters with many tenants
• What is the old behavior before changes and new behavior after changes? None

Issues Resolved

Fixes #5342
Fixes #5129

Related fix for 3.0: #5350

Testing

• Existing integration tests

Check List

• 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.
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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.13%. Comparing base (79ab0b8) to head (34e7e17).
Report is 1 commits behind head on 2.19.

Files with missing lines	Patch %	Lines
...pensearch/security/securityconf/ConfigModelV7.java	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             2.19    #5368      +/-   ##
==========================================
- Coverage   68.17%   68.13%   -0.04%     
==========================================
  Files         347      347              
  Lines       24624    24625       +1     
  Branches     4084     4084              
==========================================
- Hits        16788    16779       -9     
- Misses       5917     5930      +13     
+ Partials     1919     1916       -3     

Files with missing lines	Coverage Δ
...pensearch/security/securityconf/ConfigModelV7.java	67.98% <66.66%> (+0.06%)	⬆️

... and 6 files with indirect coverage changes

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