feat: add gnome firmware for default flatpaks (#225)

We should have a way to update firmware, gnome firmware is maintained
and shouldn't significantly add on to the ISO size as we are already
shipping bazaar and dejadup where the runtime is shared.

Author: renner0e

system_files/shared/usr/share/ublue-os/homebrew/system-flatpaks.Brewfile

@@ -8,6 +8,7 @@ flatpak "org.deskflow.deskflow"
 flatpak "org.fedoraproject.MediaWriter"
 flatpak "org.fkoehler.KTailctl"
 flatpak "org.gnome.DejaDup"
+flatpak "org.gnome.Firmware"
 flatpak "org.gtk.Gtk3theme.Breeze"
 flatpak "org.kde.gwenview"
 flatpak "org.kde.haruna"