Switch Cluster Health charts to Prometheus API endpoint
From https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27849/diffs#note_167312286
Question, does the new prometheus endpoint support the cluster health charts for EE? If this is the case we need to create an EE merge request to make sure the cluster bundle starts correctly
The Operations > Metrics page can use Prometheus endpoints to load per-chart data separately. The ** Operations > Kubernetes > Clusters** page still uses the metrics.json endpoint and loads all data at once. It should support Prom API