Add PWM2I2C setting to MQTT deviceinfo

[benjamin-dcs]

As per v2.5.0 our HA integration also provides a fan-entity. I noticed a special case in your auto-discovery code for devices which have PWM2I2C turned off:

https://github.com/arjenhiemstra/ithowifi/blob/master/software/NRG_itho_wifi/main/HADiscovery.cpp

Currently we can't automatically detect this. Could you add this to the deviceinfo topic so we can help our users by providing the right fan control?