Add Prometheus service to Athens docker-compose

**Is your feature request related to a problem? Please describe.**
As we support metrics export to prometheus (#816) we could add it as a service to our docker-compose

**Describe the solution you'd like**

There should be configured prometheus service in Athens docker-compose that will be listening on Athens metrics endpoint

**Additional context**
https://hub.docker.com/r/prom/prometheus/
https://prometheus.io/docs/prometheus/latest/configuration/configuration/