Add Minecraft onto Flathub as a Flatpak App for Linux

Hi Folks, i'd like to see mojang take over the existing wrapper (as we've seen other companies do, or simply upload their own Flatpak of Minecraft to flathub (https://flathub.org/en/apps/com.mojang.Minecraft) this is the current community maintained flatpak that packadges the app image into this format allowing it to be automatically updated and allowing for an easier install. 

1. Easier install for Linux users

2. Simplifies releases and builds for Mojang you no longer need .deb/.tar and app image you can just use one format, Flatpak which is a file format installable on all Linux systems

3. Auto updates