[FLINK-33557] Externalize Cassandra Python connector code

[ferenc-csaky]

Purpose of the change

Inspired by apache/flink-connector-kafka#69, and apache/flink-connector-aws#121. Moves cassandra.py and test_cassandra.py from the core https://github.com/apache/flink repo to this one.

When running mvn clean install, downloads the testing infra scripts from the main Flink repo:

• flink-python/dev/build-wheels.sh
• flink-python/dev/install_command.sh
• flink-python/dev/lint-python.sh

Verifying this change

The python tests can be run by the following commands:

mvn clean install -DskipTests
cd flink-python
chmod a+x dev/* 
./dev/lint-python.sh -e mypy,sphinx

[boring-cyborg]

Thanks for opening this pull request! Please check out our contributing guidelines. (https://flink.apache.org/contributing/how-to-contribute.html)

[ferenc-csaky]

@pvary @gaborgsomogyi JAR included, CI run passed.

[pvary]

QQ: Is this an uber jar for the connector?

[ferenc-csaky]

Yes, it includes the necessary cassandra related deps:

flink-connector-cassandra/flink-connector-cassandra/pom.xml

Line 367 in c541f70

<artifactId>maven-shade-plugin</artifactId>

[pvary]

The packaging part looks good.
I have limited experience with the Cassandra connector, so I would like to have someone with Cassandra experience to review it too.

[ferenc-csaky]

@echauchot Sorry to ping you out of the blue, I saw that you were an active contributor to the Cassandra connector. If you have some time, would you mind reviewing this PR? Thanks in advance!

[echauchot]

@echauchot Sorry to ping you out of the blue, I saw that you were an active contributor to the Cassandra connector. If you have some time, would you mind reviewing this PR? Thanks in advance!

Hi @ferenc-csaky it would be with pleasure but I know nothing about python so I might not be the good person to review this PR