Camera & raw-usb plugs auto-connect for qtchildid

@niemeyer - this developer is requesting auto-connection for raw-usb since it needs access to fingerprint readers and we don’t have interfaces for that. I think ultimately we want to do something along the lines of serial-port where each device is individually assignable, but that won’t help this developer until hotplug is implemented (to support classic distro). I think we have a few options:

  1. grant use of raw-usb to this snap and add /dev/biometric/sensor* (see my previous comment) to the list of things for hotplug to support
  2. write a raw-biometrics (or similar) transitional interface to give access to all /dev/biometric/sensor* devices
  3. write raw-biometrics-fingerprint, raw-biometrics-iris, etc (or similar) transitional interfaces to give access to all fingerprint, iris, and other scanners via individual interfaces

Since ‘3’ is just a more fine-grained version of ‘2’ (perhaps we would only implement fingerprint today), it may not be worth it unless hotplug is very far out.

@niemeyer, thoughts?