Fheroes2 (open Heroes of Might and Magic II) Snap package

Flatpak support isn’t installed by default on Ubuntu https://github.com/ihhub/fheroes2/blob/master/docs/INSTALL.md

Probably thousands of people are blocked from installing wanted software because installing is still simply a mess: https://www.gamingonlinux.com/2023/11/heroes-of-might-and-magic-ii-game-engine-fheroes2-v1010-released/

People use Ubuntu and appear to use its defaults en massé, so we need a Snap package for this one too.