[FLINK-25941][streaming] Only emit committables with Long.MAX_VALUE as checkpoint id in batch mode

[fapaul]

What is the purpose of the change

Before this commit the SinkWriter and Committer operators emitted
committables on endInput. This was troublesome because by doing so the
checkpointId was set to effectively null/Long.MAX_VALUE because
the emission was not part of any checkpoint. With the completion of
FLIP-143 all jobs in streaming mode have a final checkpoint when they
transition to finish so we can rely on the normal checkpoint mechanism
and only need endInput for the batch execution.

Brief change log

• CommitterOperator only emit on notifyCheckpointComplete in streaming mode
• GlobalCommitter only emit on notifyCheckpointComplete in streaming mode
• SinkWriter only emit on preSnapshotBarrier in streaming mode

Verifying this change

• Adjusted existing tests to verify the behaviour
• KafkaSinkITCase is now stable (ran 20 times locally without failure, previously it was failing every 2-3 runs)

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

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

Documentation

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

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Automated Checks

Last check on commit 5ad29aa (Tue Feb 15 15:44:08 UTC 2022)

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CI report:

• d1cccce Azure: SUCCESS

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[alpreu]

Thank you for your contribution, it looks good to me. One small nit is that the boolean value could have a better name than just 'batch'

[fapaul]

After some offline discussion I discovered that the current solution does not suffice because if users are not enabling checkpointing and run in streaming mode there is currently no way that a commit is triggered.

[fapaul]

@alpreu can you take another look I updated the PR with solution that triggers a full commit for a pipeline in streaming mode if checkpointing is not enabled.