the backlight situation will be revisited with the next board prototype,
but it's good to prove this can be done.
Depends on https://github.com/adafruit/esp32-camera/pull/6 which should
be merged before this.
this gives us a comfortable few hundred kB flash space left for the app
1398912 bytes used, 763776 bytes free in flash firmware space out of 2162688 bytes (2112.0kB).