[Backport 2.16] Caching avg total bytes and avg free bytes inside ClusterInfo

[opensearch-trigger-bot]

Backport 1305002 from #14851.

[github-actions]

❌ Gradle check result for 16e61c7: 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 16e61c7: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Attention: Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.64%. Comparing base (36dc24a) to head (16e61c7).
Report is 3 commits behind head on 2.16.

Files	Patch %	Lines
...uting/allocation/decider/DiskThresholdDecider.java	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               2.16   #14893      +/-   ##
============================================
+ Coverage     71.60%   71.64%   +0.04%     
- Complexity    62565    62595      +30     
============================================
  Files          5110     5110              
  Lines        293651   293662      +11     
  Branches      42791    42791              
============================================
+ Hits         210270   210404     +134     
+ Misses        65755    65605     -150     
- Partials      17626    17653      +27     

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