[PACKAGING] AppImage autoupdate

[RafaelLinux]

Commit Hash
1687a72

Platform
Linux

Summary
As an AppImage (Linux) user, I find more and more AppImages that auto-update itself (Upscayl, Ossia and others). As Olive is updated often (always to get a better application) would be very useful for AppImage users to have an auto-update AppImage of Olive.

[ThomasWilshaw]

Given Olive is still not stable this is outside the scope of what we're looking at just now so I'm going ot close this issue. Hopefully once Olive is stable we can look at features like this.