Export Prometheus-compatible metrics for PostgreSQL.

Plan

Per https://grafana.com/oss/prometheus/exporters/postgres-exporter/ plan could be:

• Prometheus: install https://github.com/prometheus-community/postgres_exporter (already built for FreeBSD)
• Grafana: some public dashboards use that exporer:
  • 9106 - https://grafana.com/grafana/dashboards/13576-9106-postgresql/
  • 12273 - https://grafana.com/grafana/dashboards/12273-postgresql-overview-postgres-exporter/

Deployment

In scope:

• cluster db-A

Not in scope:

• Individual containers deployed to paas-docker (but the exporter is available as container if so desired)