single container: add prometheus process

Created by: uwedeportivo

Adds prometheus in the single container deployment scenario. Follow-up PR will add grafana.

We should debate if we want to make this optional or not. I'm leaning towards keeping it in, since a future PR will expose frontend UI that shows grafana dashboards.

I have a demo container image if somebody wants to play with this. I wasn't sure where to push the image. Running it requires an additional volume arg for the prometheus data disk.