Implement "Dial In" interface

[jamesmunns]

I've discussed adding a 'dial in' interface:

1. the poststation server has a port for devices to connect to as a tcp port
2. the devices initiate the connnection
3. poststation then treats the connected device as a server, as if it had just plugged in over USB

The intent for this interface is twofold:

1. to support Ethernet or Wi-Fi based devices, like the Pico W or ESP32 devices, that will connect over TCP
2. to support third party adapters for other devices, so users can run a service on the same machine as poststation if certain interfaces are not yet included in poststation.