maxInFlightParts support for PutObject

[alextwoods]

Motivation and Context

When MultipartS3AsyncClient.putObject() performs a multipart upload of a large object, all UploadPart requests are dispatched eagerly with no concurrency limit. For example, a 2 GB upload with 8 MiB parts produces ~256 UploadPart requests that immediately compete for the HTTP connection pool (default maxConcurrency=50), leading to connection acquisition timeouts:

SdkClientException: Unable to execute HTTP request: Acquire operation took longer than the configured maximum time.

The existing maxInFlightParts configuration in ParallelConfiguration already limits concurrent GetObject requests for multipart downloads, but was not applied to the upload path.

Fixes #6623

Modifications

• Extended the maxInFlightParts configuration to also apply to multipart upload (putObject) concurrency. The setting now limits concurrent part requests for both getObject (download) and putObject (upload) operations. Updated the Javadoc on ParallelConfiguration.maxInFlightParts() to reflect this broader scope.
• In KnownContentLengthAsyncRequestBodySubscriber.onNext(): instead of unconditionally calling subscription.request(1) after dispatching each UploadPart, the subscriber now checks asyncRequestBodyInFlight < maxInFlightParts. When a part completes and in-flight count drops below the limit, subscription.request(1) resumes flow.
• Applied the same pattern in UnknownContentLengthAsyncRequestBodySubscriber.sendUploadPartRequest().
• Extracted UnknownContentLengthAsyncRequestBodySubscriber from an inner class of UploadWithUnknownContentLengthHelper into its own top-level class, matching the existing pattern of KnownContentLengthAsyncRequestBodySubscriber.

Testing

• New and existing unit tests.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.

License

• I confirm that this pull request can be released under the Apache 2 license

[alextwoods]

This warn logging was pre-existing - see the change in UploadWithUnknownContentLengthHelper that moved the existing warning into KnownContentLengthAsyncRequestBodySubscriber

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)

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