Build Cassandra 3.x connector with Java 11

Currently, that's the only component which still requires building with Java 1.8. The reason being that Cassandra Server is started in embedded mode, and it doesn't support Java > 1.8. So tests should be reworked so as to use Cassandra Server in a container (which would contain Java 1.8), allowing the connector itself to be built with Java 11 (i.e. any build config related to 1.8 can be removed from the Cassandra connector POMs).

There's two approaches for doing so:

• Use the Maven Docker plug-in (as done for most other connectors and their ITs)
• Use Testcontainers (which would make it a bit simpler to run individual tests in an IDE)

As a follow-up, we will be able to compile the entire Debezium code base to Java 11.

Related discussion: https://github.com/debezium/debezium-connector-cassandra/pull/43#issuecomment-1039294501