Fix env var password hashing for PBKDF2

[terryquigleysas]

Description

Category (Bug fix)

Passwords provided as environment variables are always hashed using BCrypt even when configured to use something else. Authentication fails when using PBKDF2 .

Issues Resolved

Resolves #4771

Testing

Initially found testing on a personal cluster. Confirmed fix works.
Included new test for PBKDF2 with PR.
Run Bulk Integration Tests.

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 67.99%. Comparing base (830b341) to head (c5349de).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...org/opensearch/security/support/SecurityUtils.java	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4773      +/-   ##
==========================================
+ Coverage   67.98%   67.99%   +0.01%     
==========================================
  Files         310      310              
  Lines       20924    20925       +1     
  Branches     3318     3319       +1     
==========================================
+ Hits        14225    14228       +3     
+ Misses       4951     4947       -4     
- Partials     1748     1750       +2     

Files with missing lines	Coverage Δ
...a/org/opensearch/security/tools/SecurityAdmin.java	48.45% <100.00%> (ø)
...org/opensearch/security/support/SecurityUtils.java	68.51% <83.33%> (ø)

... and 5 files with indirect coverage changes

[cwperks]

LGTM!