Add discovery of Freebox servers

[stilllman]

I'm in the process of developing a new device tracker platform for Home Assistant, to support Freeboxes (servers/routers provided by the french FAI Free). This PR adds the discovery of Freeboxes through mDNS, using the service specified in the API documentation.

I've tested it on my local network, here is an example of the response I got:

 freebox:
 [{'host': '192.168.0.254',
   'hostname': 'Freebox-Server.local.',
   'port': 80,
   'properties': {'api_base_url': '/api/',
                  'api_domain': '******.fbxos.fr',
                  'api_version': '5.0',
                  'device_type': 'FreeboxServer1,1',
                  'https_available': '1',
                  'https_port': '****',
                  'uid': '************'}}]

[homeassistant]

Hi @stilllman,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[balloob]

Thanks! 🐬