[Backport 2.x] Fix ShardEvents and ShardBulkDocs null metrics

[opensearch-trigger-bot]

Backport 8f5d1f1 from #283

[codecov-commenter]

Codecov Report

Merging #285 (50e7216) into 2.x (6b9df73) will increase coverage by 0.07%.
The diff coverage is 100.00%.

❗ Current head 50e7216 differs from pull request most recent head 1e3d17f. Consider uploading reports for the commit 1e3d17f to get more accurate results

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@@             Coverage Diff              @@
##                2.x     #285      +/-   ##
============================================
+ Coverage     71.89%   71.97%   +0.07%     
- Complexity     2998     3003       +5     
============================================
  Files           380      380              
  Lines         18984    18984              
  Branches       1463     1463              
============================================
+ Hits          13649    13663      +14     
+ Misses         4732     4721      -11     
+ Partials        603      600       -3     

Impacted Files	Coverage Δ
...ceanalyzer/reader/ShardRequestMetricsSnapshot.java	99.65% <100.00%> (ø)
...formanceanalyzer/reader/RequestEventProcessor.java	87.14% <0.00%> (+1.42%)	⬆️
...nsearch/performanceanalyzer/rca/RcaController.java	83.25% <0.00%> (+2.64%)	⬆️
...nalyzer/rca/net/handler/PublishRequestHandler.java	77.55% <0.00%> (+4.08%)	⬆️
...h/performanceanalyzer/reader/OSEventProcessor.java	81.94% <0.00%> (+6.94%)	⬆️

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