Add python script to install wallpapers with gnome 42 light/dark wallpaper support

[jezekra1]

Hey, I added a way to install the wallpapers as the light and dark variants in gnome settings:

Usage:

./install_gnome_42_light_dark.py [-h] bundle_name path_to_wallpapers install_dir

For example

./install_gnome_42_light_dark.py linux-dynamic-wallpapers wallpapers ~/.local/share