Tech preview support for the OpenShift Client

The OpenShift client makes it possible to write Operators or kubectl plugins in Quarkus by communicating with the OpenShift APIs. We need to add Tech preview support for this since we intend to fully support some of these use-cases in a future version and we need customers to work with these use-cases. 

Upsteam doc: https://quarkus.io/guides/kubernetes-client#openshift-client

Quickstart: None

Known issues / limitations: None (or rather, it has whatever limitations the kubernetes-client extension has)

Test coverage: https://github.com/quarkusio/quarkus/tree/master/integration-tests/openshift-client