apiextensions: add openapi publishing unit+integration+e2e tests
apiextensions: add openapi publishing unit+integration+e2e tests

Co-authored-by: Maciej Szulik <maszulik@redhat.com>
Co-authored-by: Dr. Stefan Schimanski <stefan.schimanski@gmail.com>

Kubernetes-commit: 867cdce212e4d0df9aadf207f0a9c4728dd1644a

kubernetes/apiextensions-apiserver,kubernetes/apiextensions-apiserver