Add discovery via USB

[michaelpiron]

Connection to the Eltako 14 system happens through USB, connected to the FGW14-USB module.

FGW14-USB: A USB connection to let Home Assistant send and receive messages on the EnOcean RS485 bus Manual Datasheet

Feature request: add USB discovery of the Eltako 14 system to this integration.
Related dev documentation: https://developers.home-assistant.io/docs/creating_integration_manifest#usb

Examples of discovery:

{
  "usb": [
    {
    "vid": "AAAA",
    "pid": "AAAA"
    },
    {
    "vid": "BBBB",
    "pid": "BBBB"
    },
    {
    "vid": "1234",
    "pid": "ABCD",
    "serial_number": "1234*",
    "manufacturer": "*midway*",
    "description": "*zigbee*"
    },
  ]
}