[Pull-based ingestion] Support multi-threaded writes in pull based ingestion

[varunbharadwaj]

Description

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.During shard recovery, the minimum shard pointer tracked across processor threads will be used the the start point.

Related Issues

Resolves #17875

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[github-actions]

❌ Gradle check result for bd15ddb: 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 f5027e7: TIMEOUT

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[github-actions]

❌ Gradle check result for f5027e7: 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 f5027e7: 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 f5027e7: 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?

[yupeng9]

LGTM

[github-actions]

❕ Gradle check result for 7e0dd19: 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 83.80282% with 23 lines in your changes missing coverage. Please review.

Project coverage is 72.54%. Comparing base (cbaddd3) to head (7e0dd19).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
...ndices/pollingingest/MessageProcessorRunnable.java	69.23%	6 Missing and 2 partials ⚠️
...llingingest/PartitionedBlockingQueueContainer.java	89.61%	6 Missing and 2 partials ⚠️
...rch/indices/pollingingest/DefaultStreamPoller.java	76.19%	4 Missing and 1 partial ⚠️
...g/opensearch/cluster/metadata/IngestionSource.java	77.77%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17912      +/-   ##
============================================
+ Coverage     72.51%   72.54%   +0.03%     
+ Complexity    67108    67074      -34     
============================================
  Files          5475     5478       +3     
  Lines        309916   310013      +97     
  Branches      45060    45065       +5     
============================================
+ Hits         224725   224911     +186     
+ Misses        66895    66685     -210     
- Partials      18296    18417     +121     

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