Produce apis to add a k8s cloud and tear down its models first

pytest operator supports add_k8s() method
tears down the clouds first, tearing down any models on those clouds first
tears down any other models last in reverse order they are created
allows creation of a k8s cloud given a kubernetes.client.configuration.Configuration
supports add-k8s arguments like context, skip_storage and storage_class
see test_opstest_add_k8s.py for example of how to use until I can get documentation into this
uses updated inclusivity workflow check

charmed-kubernetes / pytest-operator