[Backport 2.x] Skip unnecessary string format in RemoteStoreMigrationAllocationDecider when not in debug mode

[opensearch-trigger-bot]

Backport 5d2d392 from #16299.

[github-actions]

❌ Gradle check result for c0a634b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for c0a634b: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.72%. Comparing base (5947002) to head (c0a634b).
Report is 3 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...decider/RemoteStoreMigrationAllocationDecider.java	66.66%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #16301      +/-   ##
============================================
- Coverage     71.74%   71.72%   -0.02%     
+ Complexity    65022    64983      -39     
============================================
  Files          5302     5302              
  Lines        303866   303869       +3     
  Branches      44192    44192              
============================================
- Hits         218012   217959      -53     
- Misses        67648    67659      +11     
- Partials      18206    18251      +45     

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