[Pull-based ingestion] Support multi-threaded ingestion along with upserts and deletes

[varunbharadwaj]

Description

1. This PR adds multi-threaded writer support in the pull-based ingestion flow. The incoming message will be hashed by ID and written to one of the blocking queue partitions. A processor thread will be started to consume and process updates from each blocking queue partition. This thread will handoff the updates to the engine to update the index. Number of processor threads can be defined at the time of index creation by setting ingestion_source.num_processor_threads. If not set, a default value of 1 will be used.
2. This PR also enhances the ingestion engine to support updates and deletes. Updates/deletes work in a multi-threaded environment since updates/deletes to the same document are sequentially processed.

Note that this PR adds the framework for multi-threaded writes, but does not allow users to turn on the feature. We'll allow users to use this feature once the feature is complete and we can support atleast/exactly once processing guarantees.

Related Issues

Builds on top of #16929

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❌ Gradle check result for 5fccdaa: FAILURE

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❌ Gradle check result for 95970b5: FAILURE

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❌ Gradle check result for 69cc527: FAILURE

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❕ Gradle check result for 6330594: UNSTABLE

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[codecov]

Codecov Report

Attention: Patch coverage is 77.08333% with 33 lines in your changes missing coverage. Please review.

Project coverage is 72.48%. Comparing base (2d42bd0) to head (a68cdf7).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...a/org/opensearch/index/engine/IngestionEngine.java	21.05%	13 Missing and 2 partials ⚠️
...ndices/pollingingest/MessageProcessorRunnable.java	54.16%	8 Missing and 3 partials ⚠️
...rch/indices/pollingingest/DefaultStreamPoller.java	81.25%	2 Missing and 1 partial ⚠️
...g/opensearch/cluster/metadata/IngestionSource.java	60.00%	0 Missing and 2 partials ⚠️
...llingingest/PartitionedBlockingQueueContainer.java	97.18%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17771      +/-   ##
============================================
+ Coverage     72.39%   72.48%   +0.09%     
- Complexity    66066    66306     +240     
============================================
  Files          5358     5387      +29     
  Lines        306500   307248     +748     
  Branches      44409    44563     +154     
============================================
+ Hits         221888   222708     +820     
+ Misses        66474    66332     -142     
- Partials      18138    18208      +70     

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❌ Gradle check result for f726ea0: FAILURE

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❌ Gradle check result for c23f437: FAILURE

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❕ Gradle check result for a68cdf7: UNSTABLE

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[yupeng9]

i wonder in the corner case that the last processed message in the last batch runs into err after line 215, and also there's no new message after this message, then will this logic result in rewinding to the previous batch start pointer?

because this condition results.isEmpty() becomes true, and in the next iteration, encounteredError becomes false, then it will assume the lastProcessedPointer did not run ito error?