build appimage for linux AMD64

[pony-montana]

Appimage is the most portable distro-agnostic way to use linux binaries on machines.

[paju1986]

This will become very handy since bisq is barely on any repository

[fluse1367]

I threw a quick and dirty script together that creates an appimage: https://gitlab.com/-/snippets/3670160

(#4325, #3538, #1038)