Built-in support for appimage zsync delta updates

[FabianLars]

In tauri-apps/tauri#12491 i'll add support for zsync updates. For now this is only relevant for external appimage updaters but i think it makes sense to make our updater to support it for delta self updates as well.

[Samueru-sama]

The steps to integrate this would be the following:

• Add the zsync info to the uruntime, which for github it would be this:

ARCH="$(uname -m)"
UPINFO="gh-releases-zsync|$(echo "$GITHUB_REPOSITORY" | tr '/' '|')|latest|*$ARCH.AppImage.zsync"
./uruntime --appimage-addupdinfo "$UPINFO"

• Make the zsync file zsyncmake *.AppImage -u *.AppImage

• And release them together.

Note that the name of the AppImage or .zsync file cannot be changed after these steps are done, so that has to be taken into account.

Once this is done AppImageUpdate will be able to update any tauri appimage without issue.

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Optionally, appimageupdatetool can be bundled to allow the app to be able to self update:

• The appimage runtime already sets the env variable APPIMAGE which contails the full path to the AppImage with symlinks resolved. So all that needs to be done is run appimageupdatetool -Or "$APPIMAGE" once the user chooses to update the app.

appimageupdatetool would have to be bundled, however the upstream version is very big at at 38 MiB for a cli tool because they decided to ship debugging info into the thing xd

The version we have is 5.67 MIB and I can make a separate fork that only changes the build process, since this fork has other changes on top like using a proxy to bypass github API limits, which really isn't needed in this use case. I can also try building it on alpine which should make it even smaller.