[FLINK-23748][tests] Testing window TVF session window

[hililiwei]

What is the purpose of the change

Add the SESSION Window TVF followed by Window Aggregate test class

https://issues.apache.org/jira/browse/FLINK-23748

Brief change log

Add Session Windows test methods in WindowAggregateITCase, including GroupingSets, Cube, Rollup, etc

Verifying this change

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? no
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Automated Checks

Last check on commit cbd5815 (Sat Sep 04 01:56:44 UTC 2021)

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• ❓ 5. Overall code [quality] is good.

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CI report:

• cbd5815 Azure: FAILURE

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