Add model SmartMI Evaporative Humidifier 2 (zhimi.humidfier.ca4)

[jbouwh]

If you are receiving a warning indicating an unsupported model (Found an unsupported model '<model>' for class '<class>'.),
this means that the implementation does not list your model as supported.

If it is working fine for you nevertheless, feel free to open an issue or create a PR to add the model to the _supported_models (example) for that class.

Before submitting, use the search to see if there is an existing issue for the device model, thanks!

Device information:

• Name(s) of the device: SmartMI Evaporative Humidifier 2
• Link: https://xiaomi-mi.com/air-and-water-purifiers/xiaomi-smartmi-air-humidifier-2-white/

Use miiocli device --ip <ip address> --token <token>.

• Model: zhimi.humidifier.ca4
• Hardware version: esp32
• Firmware version: 2.1.8

There are no issues known to me.

[jbouwh]

Triggered by Home Assistant:
Found an unsupported model 'zhimi.humidifier.ca4' for class 'AirHumidifierMiot'. If this is working for you, please open an issue at https://github.com/rytilahti/python-miio/