[FLINK-20508][python] Introduce PythonStreamGroupTableAggregateOperator

[HuangXingBo]

What is the purpose of the change

This pull request will introduce PythonStreamGroupTableAggregateOperator

Brief change log

• Add PythonStreamGroupTableAggregateOperator
• Add base class AbstractPythonStreamAggregateOperator

Verifying this change

This change added tests and can be verified as follows:

• Added UT in PythonStreamGroupTableAggregateOperatorTest

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/Mesos, 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)

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Automated Checks

Last check on commit 86e97e7 (Mon Dec 07 12:24:09 UTC 2020)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!
• This pull request references an unassigned Jira ticket. According to the code contribution guide, tickets need to be assigned before starting with the implementation work.

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Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

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CI report:

• 86e97e7 Azure: SUCCESS

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[dianfu]

LGTM. Merging...

[dianfu]

@internal

[dianfu]

@internal

[dianfu]

@internal