[FLINK-22702][tests] Add test data supplier which use null timestamp field to kafka connector tests

[ruanhang1993]

What is the purpose of the change

This pull request add new test data generator to the kafka connector test cases, it supports generating data without timestamps. Besides that, we are able to supply different ways to generate test data.

Brief change log

• add test data generating function which don't need timestamps to KafkaSourceTestEnv
• modify setupTopic method in KafkaSourceTestEnv, support supplying a function to generate test data
• modify the related code wihch used the setupTopic method

Verifying this change

This change is already covered by existing tests

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? (no)

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Last check on commit c851c63 (Wed Aug 25 02:06:41 UTC 2021)

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[becketqin]

Thanks for the patch. LGTM.
Merged to master: 83b9ee8