Config for built-in web-server

[ppo]

Please allow to configure the domain and port for the built-in server.

For example by adding in config/system.yaml something like:

server:
  host: project-name.test
  port: 3000

So that executing bin/grav server will result in:

[OK] Built-in PHP web server listening on http://project-name.test:3000 (PHP v8.2.4)