Support for kubectl during registry operator testing

[michael-valdron]

/kind user-story

Which area this user story is related to?

/area registry

User Story

As a contributor, I want to use minikube, so that I can test my changes with Kubernetes.

Currently, the registry operator integration test suite only supports the use of oc, https://github.com/devfile/registry-operator/blob/fd4aacc91609bdb18891ce9aeeeb99e439afac03/tests/integration/pkg/client/oc.go. This means though one can still run their integration tests on a Kubernetes cluster it does require that the developer has OpenShift CLI client oc installed. Since the registry operator supports both OpenShift and Kubernetes this should not be a requirement for testing.

Acceptance Criteria

• Create the same client functions for kubectl
• Add control logic for all client function invokes to determine which tool to use
  • This could be just if oc is installed and fail if both are not installed