This group has access to modifying backlight settings (configured by
the udev rules for `light`).
Change-Id: I1593980757c6265f6822d3d3dce9e19a2473acd8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2626
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>