[Pull-based Ingestion] add basic NodeStats metrics

[xuxiong1]

Description

This PR adds the basic NodeStats metrics to pull-based ingestion.

• Added total polled and total processed message count metrics, as part of IndexShardStats.
• Tested in the Kafka integration test
• TODO: add metrics for error handling and consume lag.

Related Issues

Resolves #17077

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❌ Gradle check result for a3eeb6a: FAILURE

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❌ Gradle check result for e9ab1ee: FAILURE

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❌ Gradle check result for 8ddd871: FAILURE

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❌ Gradle check result for 47c124b: FAILURE

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❌ Gradle check result for 45f680d: FAILURE

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❌ Gradle check result for 17db713: FAILURE

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✅ Gradle check result for 17db713: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 71.76471% with 24 lines in your changes missing coverage. Please review.

Project coverage is 72.45%. Comparing base (0ffed5e) to head (17db713).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
...arch/indices/pollingingest/PollingIngestStats.java	78.57%	3 Missing and 9 partials ⚠️
...rch/indices/pollingingest/DefaultStreamPoller.java	33.33%	4 Missing ⚠️
...nsearch/action/admin/indices/stats/ShardStats.java	62.50%	2 Missing and 1 partial ⚠️
...in/java/org/opensearch/indices/IndicesService.java	0.00%	2 Missing ⚠️
...min/cluster/stats/TransportClusterStatsAction.java	50.00%	1 Missing ⚠️
...a/org/opensearch/index/engine/IngestionEngine.java	0.00%	1 Missing ⚠️
...ndices/pollingingest/MessageProcessorRunnable.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17444      +/-   ##
============================================
+ Coverage     72.42%   72.45%   +0.02%     
- Complexity    65611    65645      +34     
============================================
  Files          5304     5307       +3     
  Lines        304743   304678      -65     
  Branches      44189    44174      -15     
============================================
+ Hits         220701   220743      +42     
+ Misses        65888    65881       -7     
+ Partials      18154    18054     -100     

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