Add support for ZeroConf discovery

[egguy]

Hello,

I've added the support for discovering the overkiz box by ZeroConf.

The entry is: _kizbox._tcp.local.

There's a properties attribute which contain directly the gateway ref (aka gateway_pin).

[iMicknl]

Thanks! Could you add a test as well? Since core has the requirement for 100% test coverage config flow, we require that for config flow as well.

If you want, you could also see how you can bring this to core yourselves as well. See #697. The config flow in core has some slight changes though.

[iMicknl]

Thanks! Would you like to do a PR to core as well, with this functionality? If you need help setting up core dev environment, I am happy to help.