A minimal CI setup (pipeline) exists to test tektoncd/operator on openshift

At present, there is no way to run upstream tektoncd/operator tests agains openshift 4.x clusters.

Therefore, there should be a absolute minimum setup to make sure that e2e tests of operator are run on OpenShift. (The set up could be improved after code freeze)

Acceptance Criteria

• a pipeline exists which can create openshift-4.6 (or 4.7) clusters and run unit tests, build tests, e2e tests
• a workflow (manual) exists using which developers can run tests from upstream 'main' branch and from new PRs against OpenShift