Add PortForward section to skaffold config for externally built containers

[marcinc]

Currently skaffold dev doesn't tail logs or port-forwards services that aren't build by skaffold. See relevant issue: GoogleContainerTools/skaffold#5067

Alternative solution would be to explicitly inject (and reconcile) portForward config section for relevant services, e.g.:

portForward:
  - resourceType: Service
    resourceName: wordpress
    namespace: wp
    port: 8080
    localPort: 8080