Update Prometheus Metric Library to support multiple series and colors
Now that we have support for additional colors and series (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14100) we need to update the Prometheus queries to take advantage.
We should:
- Adjusts the queries to now support returning multiple series where it makes sense. (CPU utilization, throughput)
- Updates the documentation for the new queries, and improves the nginx-ingress configuration guide.