Replace in-process ConnectCluster with StrimziConnectCluster in operator tests

[see-quick]

Remove ConnectCluster.java, TestingConnector.java, and the connect-runtime/connect-file/connect-api dependencies from the operator. Update KafkaConnectApiIT and KafkaConnectorIT to use StrimziConnectCluster with .withStrimziFaultInjectionSourceConnector(). Depends on sub-issue strimzi/test-container#216 being released.