Prometheus: Listen on 0.0.0.0

[velvia]

Really simple one line fixes. The old value was 127.0.0.1 which prevents metrics from listening on external connections.

I could expand this to use ValidatorConfig for validators if @bmwill could show me how to convert multiaddr to SocketAddr, but I couldn't' find an easy way, and we're just trying to get this working quickly for observability.

[bmwill]

@velvia Yeah i did add a, currently unused, metrics address to the ValidatorConfig. We can add the ability to convert the Multiaddr to a socket addr and then use it in a future PR.

[velvia]

Thanks @bmwill I just didn't know how to convert to SocketAddr, I didn't find anything tin the MultiAddr docs.rs... a third party crate seemed to do it but didn't think it made sense to bring in another crate just to do conversion, thought you might know a better way.

Or we can just go back to host and port config. :-p