[FLINK-14729][connectors] Multi-topics consuming from KafkaTableSource

[fangpengcheng95]

What is the purpose of the change

propose a new functionality of KafkaTableSource which can consume multiple topics at the same time.

Brief change log

Design plan

Add a new constructor in KafkaTableSource which accepts topics with List type as one parameter.
Modify the existed one which only accepts one topic as string type to call the proposed one to finish the instantiation. That is to say, wrap this topic in a list and pass it to the multi-topics-consuming constructor.
Modify the overridden method createKafkaConsumer in KafkaTableSource to pass topics as List instead of String.
Replace the field topic with topics as List type in  KafkaTableSourceBase and modify every place using topic with topics. So we just need to modify the constructor KafkaTableSourceBase, method getDataStream, and equals and hashCode.

Verifying this change

Test plan

There is less to do as KafkaTableSource is based on FlinkKafkaConsumer which already supports consuming multiple topics and is tested well. Of course, we can easily add further more tests if needed.

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, Yarn/Mesos, 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 31a5d3d (Wed Dec 04 15:09:23 UTC 2019)

Warnings:

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

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CI report:

• 42fbaee : FAILURE Build
• 0b76557 : FAILURE Build
• 28e8bc1 : FAILURE Build
• 31a5d3d : FAILURE Build

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[fangpengcheng95]

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[fangpengcheng95]

This is my first PR，can someone give any reviews，thx~ @wuchong
@GJL @zentol