add Appimages builds

[eadmaster]

I prefer Appimages over flatpaks because they are easier to install.

Also mentioned here.

[Murmele]

@eadmaster currently there is no plan for it. The problem is then we have to maintain another package. I think this has to be done by somebody externally. We will help of course if possible

[Murmele]

There is a pr pending, I have to finalize it and get it work on RHEL9