Extracted the user attr handling methods from ConfigModelV7 into its own class

[nibix]

Description

This code change is just in preparation for the change in #4380 as requested in #4380 (comment) .

The code for user attribute handling is moved from the class ConfigModelV7 into its own class, as other new code will need to use it. Additionally, it enhances the structuring of the code by moving code with a specific purpose into its own class.

Personal note: A thorough re-design of this code might be worthwhile.

• Category: Refactoring
• Why these changes are required? New code introduced in Optimized Privilege Evaluation #4380 needs to use this code.
• What is the old behavior before changes and new behavior after changes? No behavioral changes.

Issues Resolved

• Optimized Privilege Evaluation #4380 (comment)

Is this a backport? If so, please add backport PR # and/or commits #

Testing

[Please provide details of testing done: unit testing, integration testing and manual testing]

Check List

• New functionality includes testing - no new functionality
• New functionality has been documented - no new functionality
• 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 78.57143% with 6 lines in your changes missing coverage. Please review.

Project coverage is 65.45%. Comparing base (8688d6b) to head (4695280).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4416      +/-   ##
==========================================
+ Coverage   65.42%   65.45%   +0.02%     
==========================================
  Files         310      311       +1     
  Lines       22013    22014       +1     
  Branches     3556     3556              
==========================================
+ Hits        14402    14409       +7     
+ Misses       5841     5836       -5     
+ Partials     1770     1769       -1     

Files	Coverage Δ
...pensearch/security/securityconf/ConfigModelV7.java	67.92% <100.00%> (-0.47%)	⬇️
...opensearch/security/privileges/UserAttributes.java	76.00% <76.00%> (ø)

... and 5 files with indirect coverage changes

[shikharj05]

Thanks! I also like the idea of breaking #4380 down into such PRs to make the review faster. Feel free to raise such incremental PRs :)

[peternied]

Since this is a refactor, let's just move in place.

@shikharj05 - want to make a follow up PR for some of those items you called out.