Add OARS rating for parental controls. https://odrs.gnome.org/oars

This is part of the fix for https://invent.kde.org/kde/kaidan/issues/312 it adds open ratings markup that allows software stores to put age ratings on the app or parental controls systems to know more about an apps capabilities and rating. Adding the markup is a Flathub requirement and is something we've been slowly adding to all KDE apps.