[Feature] Making AppImages updateable

[Ultrabenosaurus]

• Etcher version: all
• Operating system and architecture: Manjaro linux 6.11.10
• Image flashed: N/A
• What do you think should have happened: AppImageUpdate and AppImageLauncher should be able to update the balenaEtcher AppImage program, or it should be able to update itself, without downloading the entire ~150MB release
• What happened: I am stuck on 1.81.4 with no way to update-in-place, and I must download the entire 150MB new AppImage
• Do you see any meaningful error information in the DevTools? no

I would like to suggest that the AppImage releases be made updateable, per the AppImage spec:

https://docs.appimage.org/packaging-guide/optional/updates.html

This would allow users to receive updates without having to re-download the entire program, and would also allow the AppImages to update themselves internally.

This has been requested here a few times in the past, but all Issues are closed without a declaration or reason that it won't be done, but it is not currently implemented.