[Core/ZHA] Investigate sub-device support #73
Description
Other integrations like Shelly in Home Assistant support sub-devices. So, a two-gang relay/switch is exposed as two sub devices.
This is something we should look into for ZHA.
Some outstanding questions:
- How many Zigbee devices use multiple endpoints when they should not?
- Can this be done automatically or are explicit quirks definitions needed?
- ...