config: Add more game making tools to default apps

In apps_add for flatpak-remote-flathub, add the following:

- com.github.libresprite.LibreSprite
- com.unity.UnityHub
- io.gdevelop.ide
- org.godotengine.Godot

This change will apply to any images which use the default list of apps.

https://phabricator.endlessm.com/T34960

config/defaults.ini

@@ -507,9 +507,12 @@ apps_add =
   com.endlessnetwork.passage
   com.endlessnetwork.tankwarriors
   com.endlessnetwork.whitehouse
+  com.github.libresprite.LibreSprite
   com.tux4kids.tuxmath
   com.tux4kids.tuxtype
+  com.unity.UnityHub
   edu.mit.Scratch
+  io.gdevelop.ide
   io.lmms.LMMS
   io.thp.numptyphysics
   org.audacityteam.Audacity
@@ -519,6 +522,7 @@ apps_add =
   org.gnome.Gnote
   org.gnome.Rhythmbox3
   org.gnome.Weather
+  org.godotengine.Godot
   org.inkscape.Inkscape
   org.kde.gcompris
   org.laptop.TurtleArtActivity