We now work with Ingress from the API group networking.k8s.io. Ingress
in the extensions API group is no longer supported. This entails:

- update RBAC grants
- update client-go code
- update the examples/tests, currently only using helm deployments
  - changes in the Ingress backend and service fields
  - for now we only test pathType:ImplementationSpecific, implemented
    as posix_type re2 matches, which had been the match implementation
    prior to this change.

viking will support the Match and Prefix pathTypes, but in this
iteration, it was not necessary to change the code to support the
ImplementationSpecific pathType.

Examples/tests with kubectl deployments and plain YAML manifests will
also be updated in an upcoming iteration.