test(e2e): detect local cluster for local e2e tests

[TheSpiritXIII]

Reintroduces code from last year to detect the local cluster.

This allows you to run a single test locally, e.g. via go test or your IDE.

This is a minimal PR:

• You must clean-up your cluster manually before and after the test, e.g. kubectl delete -f manifests/operator.yaml && kubectl delete -f manifests/setup.yaml.
• You cannot run multiple tests due to the above restriction.
• You must build your image manunally before the test, e,g, DOCKER_PUSH=1 make operator.