create cli and/or environment variables to change default port for services

[jvalinsky]

It would be nice to be able to change the default port for services, especially in systems like NixOS where containers aren't always used. Additionally if you run more than one service on the same server then there's a port conflict for Prometheus metrics.

If you are ok with this change, what preferences do you have? Thanks.

[uniphil]

i'm happy to pick up any normal-ish --port P --host H or --bind whatever style convention you like!

metrics: yeah would be good to add a second arg here, --metrics-port or --bind-metrics etc., and probably actually avoid starting the prometheus server if it's not set.

(adding conditional prom server starting is not at all required for me to accept a PR just putting port args in though!)

[uniphil]

constellation now has configurable bindings:

Options:
      --bind <BIND>
          constellation server's listen address [default: 0.0.0.0:6789]
      --bind-metrics <BIND_METRICS>
          metrics server's listen address [default: 0.0.0.0:8765]

need to add for most of the other services still but it's a start :)