usr/share/backgrounds: add some wallpapers

I am donating these pictures to the Universal Blue project. Should
you want to use these in Bazzite, feel free to. I hope these can
give users some joy in the default config. These are some of my
favorite pictures and sharing is caring.

Please let me know if you want more, I'm sure I can dig some up.

All of these except foothills.jpeg were shot on a Canon EOS R10.

Please let me know if I should lower the JPEG quality.

Signed-off-by: Xe Iaso <me@xeiaso.net>

usr/share/backgrounds/clouds.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
+<wallpapers>
+    <wallpaper>
+        <name>The Cloud(s)</name>
+        <filename>/usr/share/backgrounds/clouds.jpeg</filename>
+        <options>zoom</options>
+        <shade_type>solid</shade_type>
+        <pcolor>#000000</pcolor>
+        <scolor>#ffffff</scolor>
+    </wallpaper>
+</wallpapers>

usr/share/backgrounds/foothills.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
+<wallpapers>
+    <wallpaper>
+        <name>LA Foothills</name>
+        <filename>/usr/share/backgrounds/foothills.jpeg</filename>
+        <options>zoom</options>
+        <shade_type>solid</shade_type>
+        <pcolor>#000000</pcolor>
+        <scolor>#ffffff</scolor>
+    </wallpaper>
+</wallpapers>

usr/share/backgrounds/space_needle.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
+<wallpapers>
+    <wallpaper>
+        <name>Space Needle</name>
+        <filename>/usr/share/backgrounds/space_needle.jpeg</filename>
+        <options>zoom</options>
+        <shade_type>solid</shade_type>
+        <pcolor>#000000</pcolor>
+        <scolor>#ffffff</scolor>
+    </wallpaper>
+</wallpapers>

usr/share/backgrounds/sunset.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
+<wallpapers>
+    <wallpaper>
+        <name>Sunset</name>
+        <filename>/usr/share/backgrounds/sunset.jpg</filename>
+        <options>zoom</options>
+        <shade_type>solid</shade_type>
+        <pcolor>#000000</pcolor>
+        <scolor>#ffffff</scolor>
+    </wallpaper>
+</wallpapers>