Linux: Publish metadata to releases #39
Description
Rather than requiring cloning the whole repo for Linux/Flatpak builds, we can publish the metadata alongside the PCK file. Then e.g. in a Flatpak manifest, we can just point to the published PCK and metainfo bundle to do everything we need.
In theory, this should speed up Flatpak builds and waste less bandwidth downloading things we don't need (like the source code and all of the in-game assets which are already included in the PCK file).