feature request: per-monitor brightness control

I know there are plenty of utilities that can do brightness control for laptops, but especially doing it for external monitors with ddc/ui can be tricky, since some monitors expose the Brightness value as X10, others the Gamma as X6B, etc. KDE and gnome now both have added an easy way to adjust per-monitor-brightness-control, so it might be sensible to add that here as well, either through a standalone implementation, or by choosing a backend.