This changes the `validator` role to create a configuration for a
network exposed validator. The previous setting, where
`--role validator` set the parameters for an isolated validator behind a
`sentry` mode can now be configured by using
`--role isolated-validator`.

This is now more in line with the setup used in
https://github.com/shutter-network/snapshot-keyper which means less
configuration changes are needed during the setup.

It also allows for a simpler local docker compose test setup.