[proxyd] Allow Prometheus to connect to an external instance instead of only itself

[DefiDebauchery]

Is your feature request related to a problem? Please describe.
I'm interested in keeping an eye on the metrics provided by proxyd. I intend to run several instances of proxyd, but because each proxyd instance has a self-contained Prometheus server, that also means several disparate instances of Prometheus.

Describe the solution you'd like
Allow the ability for proxyd to connect to be a client of an external Prometheus connection
Add a configurable namespace so that data from several networks can be properly stored