testing/calamares: new aport

I've been working on making a Alpine Linux live USB for a while which uses Calamares to install the system. There is still work to do with the install scripts, but Calamares itself works.

I'm submitting this now mainly so postmarketOS (and possible other Alpine derivatives) can use it, but I'll make a calamares-alpine package later for the Alpine Linux specific configuration.

CC @ollieparanoid, you've been developing the Calamares based installer on pmOS based on my APKBUILD for it, and I've adopted my APKBUILD with your changes. Since you made it configurable, this should be good enough to use on postmarketOS as well. Does it look good for you like this?