Draft: main/postmarketos-ui-lxqt: save and restore brightness on boots
This MR adds the tool brightnessctl
to LXQt to save and restore display brightness across boots. See commit message for more details.
Additionally splitting the post-install scripts into two because one is general and the other is for OpenRC.
The MR is similar to !5655 (closed) but doesn't have additional changes on the settings of LXQt.