[FLINK-9001] [e2e] Add operators with input type that goes through Kryo serialization

[tzulitai]

What is the purpose of the change

This PR is based on top of #7041. Only the last commit relevant.

This PR extends coverage of our all-round DataStream end-to-end test job to have operators with input types that goes through Kryo serialization:

• Without the data type registered
• With the data type registered
• With the data type registered, also with a custom Kryo serializer

Verifying this change

All end-to-end tests should still pass with the change.

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)

[twalthr]

Thank you @tzulitai. I added one comment.

[twalthr]

Should we also pass the expected serializer class to this method or some validation lambda that takes the serializer such that we can perform some validation to make sure we are testing the right thing?

[twalthr]

@tzulitai any news here?

[tillrohrmann]

Close as abandoned.