[FLINK-37112] Support Event Time Extension in DataStream V2

[codenohup]

What is the purpose of the change

Support Event Time by Generalized Watermark in DataStream V2

Brief change log

More information see FLIP-499:
https://cwiki.apache.org/confluence/x/pQz0Ew

Verifying this change

This change added tests and can be verified as follows:

• Add integration test cases, org.apache.flink.test.streaming.api.datastream.extension.eventtime.EventTimeExtensionITCase
• Add unit test cases

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? I will add documentation in a future pull request.

[flinkbot]

CI report:

• 9855bda Azure: SUCCESS

Bot commands

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• @flinkbot run azure re-run the last Azure build

[reswqa]

Thanks for the update, only left two minor comments.

[reswqa]

Thanks for the update.