Draft: Include Meadow wallpapers and switch to it for Weston

We still need to change the wallpaper for all other UIs (I'm also not sure we've settled on which wallpaper to use for v23.12 yet?), but I wanted to open this as a draft to gather feedback on the approach. I took inspiration from Fedora where every release's wallpapers are in separate packages and as such wallpapers from older releases can be installed on newer ones if you like them without having to clutter the wallpaper selection with wallpapers from literally every release.

Related: #2499