[FLINK-38096] AsyncSinkWriter may hang when configured with a custom rate limiting strategy

[HundalTaran]

What is the purpose of the change

In Async Writer, records are getting stuck on executing rate limiting. So, need to make sure that write should wait only if records are present in flight.

Brief change log

Changed in method of AysncWriter.java class from mailboxExecutor.yield(); to yieldIfThereExistsInFlightRequests();
Also. added junit to cehck this yielding.
An example is provided with bucket4j to test rate limiting scenario.

Verifying this change

Existing junits are getting passed.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)- no
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no) - no
• The serializers: (yes / no / don't know) - no
• The runtime per-record code paths (performance sensitive): (yes / no / don't know) - no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know) - no
• The S3 file system connector: (yes / no / don't know) - no

Documentation

• Does this pull request introduce a new feature? (yes / no) -no
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)- not applicable

[flinkbot]

CI report:

• 2458425 Azure: FAILURE

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[davidradl]

Unapproved licenses

   flink-examples/base-connector-examples/src/main/java/org/apache/flink/TokenBucketRateLimitingStrategy.java
  flink-examples/base-connector-examples/src/main/java/org/apache/flink/TokenBucketProvider.java
  flink-examples/base-connector-examples/src/main/java/org/apache/flink/AsyncSinkHangDemo.java
  flink-examples/base-connector-examples/src/main/java/org/apache/flink/DummyAsyncSink.java