Adjust monitor-net settings

[frenchu]

Assigning a static address for monitor-net can lead to an issue. User can run other compose projects and create custom networks. By default docker will assign random network addresses automatically. When user already has a docker network with the same address as monitor-net address, rocketpool services are not starting:

 ✘ Network rocketpool_monitor-net  Error                                                                                                     0.0s
failed to create network rocketpool_monitor-net: Error response from daemon: cannot create network b5fe819f2eb9d83d916309fcacde43fc22a08368ab9f083be13ac9e0baaa5891 (br-b5fe819f2eb9): conflicts with network dff50a78ca4140c6ccef48a845397cbea6a38833bb1b35f4b68bd6777dd4bd7f (br-dff50a78ca41): networks have overlapping IPv4
exit status 1

Moreover, Grafana service can be isolated from containers in rocketpool_net and connected to monitor-net with Prometheus service.

More details in the pull request comments.