Add AppImage building

[Mar0xy]

This would be really helpful for Fedora and OpenSuse users as ALVR itself already builds an AppImage but ALXR doesn't have appimage builds yet which makes it basically extremely hard to use on both Distros and on opensuse in fact basically as nearly as impossible.

[korejan]

@Mar0xy Hello, do you mean the ALVR server? please note the linux builds of ALXR are also clients, all the builds are all clients. The windows/linux build is typically meant for streaming to wired/diy headsets.

[Mar0xy]

Yes I indeed meant the server as the ALVR server is also available as an appimage (though it has a web interface)

[korejan]

@Mar0xy m00n made the appimages for the alvr server, there is an appimage of v18.2.3 here but I've never tested it or heard anyone using it.

[Mar0xy]

I have seen it float around reddit a few times sadly if you try launching it it just breaks and gets stuck on "waiting on server"