Refactor remaining controller/webhook unit tests into integration ones

[danail-branekov]

Controllers in statefulset-runner, kpack-image-builder and job-task-runner are still a mixture of unit and integration tests. Let's clean this up and only have oneflavour of testing those things - an integration test.

While workingon that, make sure to split controllers/webhooks in separate packages (as long as that makes sense) in order to simplify test setup and the very test (see #3304)