[Backport 2.x] Fix env var password hashing for PBKDF2

[opensearch-trigger-bot]

Backport 199662e from #4773.

[codecov]

Codecov Report

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

Project coverage is 65.43%. Comparing base (7ebcc00) to head (44200b1).
Report is 3 commits behind head on 2.x.

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

Additional details and impacted files

@@            Coverage Diff             @@
##              2.x    #4778      +/-   ##
==========================================
- Coverage   65.44%   65.43%   -0.02%     
==========================================
  Files         319      319              
  Lines       22252    22252              
  Branches     3594     3595       +1     
==========================================
- Hits        14563    14560       -3     
  Misses       5887     5887              
- Partials     1802     1805       +3     

Files with missing lines	Coverage Δ
...a/org/opensearch/security/tools/SecurityAdmin.java	41.46% <100.00%> (ø)
...org/opensearch/security/support/SecurityUtils.java	68.51% <83.33%> (ø)

... and 3 files with indirect coverage changes