Grafana datasource: prometheus

Configuring prometheus as a grafana datasource.

Documentation

getting started	https://grafana.com/docs/grafana/latest/getting-started/get-started-grafana-prometheus/
official docs	https://grafana.com/docs/grafana/latest/datasources/prometheus/

TODO:

• using query options (bottom left) to override query-line name
• using query options to switch between from range to instant to get counts
• $__range vs $__interval vs $__rate_interaval