Provide aarch64 binaries

[orowith2os]

This would allow vpuppr to run on ARM64 devices, like the Raspberry Pi 4 and M1 macs (running Asahi, at the very least).

The original idea for this was to add a source that pulls in the aarch64 binaries rather than x86_64 if running on an aarch64 system to the Flatpak manifest, so that it could work on devices like the Raspberry Pi 4. This seems to be possible, as flatpak manifests support using only-arches.