[FLINK-12820][Connectors / Cassandra] Support ignoring writing nulls

[ozancicek]

What is the purpose of the change

Added support to ignore null fields when writing to c* for tuple types.

Brief change log

• Added 'ignoreNullFields' config parameter which can be enabled
• Unset nulls from bound statement.

Verifying this change

This change added tests and can be verified as follows:
Added a test case to CassandraConnectorITCase testing partial column updates

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, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (yes)
• If yes, how is the feature documented? (JavaDocs)

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Review Progress

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

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[StephanEwen]

@flinkbot approve-until architecture

[StephanEwen]

Overall approach looks good.

I would ask you to switch to use primitive booleans rather than boxed booleans, to be consistent with the approach in the remainder of Flink. This also avoid accidental nullability and late null pointer exceptions.

Otherwise looks good to me.

[StephanEwen]

@flinkbot approve all

[StephanEwen]

Looks good to me, merging this...