dockerhub: proxy grafana/ images

The grafana-operator creates Grafana pods from docker.io/grafana/grafana,
which the dockerhub remote did not allow, so the pods would ImagePullBackOff.
Add the ^grafana/ pattern so the grafana image (and image-renderer) proxy
through artifactapi.

config/remote_docker/dockerhub.yaml

@@ -16,6 +16,7 @@ patterns:
   - "^bitnami/"
   - "^curlimages/curl"
   - "^emberstack/kubernetes-reflector"
+  - "^grafana/"
   - "^hashicorp/consul"
   - "^hashicorp/vault"
   - "^intel/"