[BUG] [Streaming Indexing] Fix intermittent "The bulk request must be terminated by a newline [\\n]" failures

[reta]

Describe the bug

While bulk ingesting more or less large documents (> 1Kb), the server may reply intermittent with:

{"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"The bulk request must be terminated by a newline [\\n]"}],"type":"illegal_argument_exception","reason":"The bulk request must be terminated by a newline [\\n]"},"status":400})

The issue comes from the fact that Netty could emit chunks partially but have knobs to control this behaviour. This configuration is not exposed by Reactor Netty yet (see please reactor/reactor-netty#3452) but expected to come in the next minor release.

Related component

Indexing

To Reproduce

See please https://build.ci.opensearch.org/job/gradle-check/47073/testReport/org.opensearch.rest/ReactorNetty4StreamingIT/testStreamingRequestOneBatchBySize/

Expected behavior

The large documents should be bulk indexed normally

Additional Details

Plugins
transport-reactor-netty4

Screenshots
If applicable, add screenshots to help explain your problem.

Host/Environment (please complete the following information):

• CI

Additional context
reactor/reactor-netty#3452

[reta]

@thomas-long-f3 fyi

[bharath-techie]

[Triage attendees - 1 2 3 4]