Switch back to a Junit extension for session management in GraphQL

[olim7t]

Stargate v1 integration tests use a Junit 5 extension for tests that need the Java driver: CqlSessionExtension.

When I ported the GraphQL API to Quarkus, there was a point where getting the coordinator address was complicated from an extension, so I used a parent class instead: CqlEnabledIntegrationTestBase.

But the test infrastructure has evolved since then, and the address is now in a system property, easy to get from anywhere (via IntegrationTestUtils.getCassandraCqlAddress()). So it looks like CqlSessionExtension would be pretty easy to port after all.

This is a cleaner approach so we might want to take the extra effort to do it. But note that this is not high priority: the parent class approach works fine, and it's only used in the GraphQL API at the moment.