[Task] CI should build Cryostat 3.0, not 2.x

[andrewazores]

Currently the CI setup for each PR builds Cryostat 2.5.0-snapshot to check for regressions or breakages. This should build 3.0.0-snapshot instead, which comes from a separate repository.

[andrewazores]

Actually, the CI builds both. I think just dropping the 2.x side would be appropriate now - there are breaking changes made in -core which we will not carry forward for 2.4.1 or any future unplanned 2.x release. Anything further that goes into 2.4.1 or beyond at this point will go in via backports to existing upstream branches.