Default to Adwaita wallpapers

[cassidyjames]

e.g. set org.gnome.desktop.background picture-uri to file:///usr/share/backgrounds/gnome/adwaita-l.webp and picture-uri-dark to file:///usr/share/backgrounds/gnome/adwaita-d.webp.

[cassidyjames]

I guess match what's in /usr/share/gnome-background-properties/adwaita.xml:

<?xml version="1.0"?>
<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
<wallpapers>
  <wallpaper deleted="false">
    <name>Default Background</name>
    <filename>/usr/share/backgrounds/gnome/adwaita-l.webp</filename>
    <filename-dark>/usr/share/backgrounds/gnome/adwaita-d.webp</filename-dark>
    <options>zoom</options>
    <shade_type>solid</shade_type>
    <pcolor>#3071AE</pcolor>
    <scolor>#000000</scolor>
  </wallpaper>
</wallpapers>