Don't depend on $port if using auto devops

Clearly configure a config.workhorse.configured_port when using auto_devops (or nginx).

We still retain the ability to use config.port if neither auto_devops nor nginx is enabled

Breaking

• This removes config.nginx.workhorse_port from gdk.yml. Please switch to using config.workhorse.configured_port
• You can no longer use port=8081 gdk run. Instead configure config.workhorse.configured_port in your gdk.yml instead then gdk reconfigure.