Add configuration file for HKCam

[pieter]

This makes it easy to change options like minimum bit rate, camera rotation and pairing PIN, without having to actually SSH into the device.

Will make some issues easier to configure, like #4 and #22

[brutella]

I like the idea of adding configuration options to ansible. Not sure if a text file in the boot partition is the best way.

If we use ansible to create the configuration file, why not use ansible variables. Take a look at the disable_camera_led variable as a reference.

[pieter]

Reason of putting it in the boot partition was that everyone can change this after flashing the OS to their device -- no need to install & run ansible to update the config. The boot partition is available on Linux / Windows etc. as well, so you can update the config in the same way as you set up the WiFi credentials.

[brutella]

Thanks 🎉