Consider adding prometheus configuration values to Ursula configuration file.

[derekpierre]

At the moment prometheus configuraiton values are only CLI options and not part of the Ursula configuration file.

For prometheus, the available CLI options for customizing it are:

--prometheus --metrics-port <> --metrics-interval <>

Consider storing these in Ursula's configuration file, instead of needing them to be explicitly specified for nucypher ursula run.

(Not sure if this is necessarily 7.3.x but rather some other future version, but putting there for now for visibility)