Include Alpine into rpi-imager

rpi-imager is now default multi-platform tool from Pi Foundation to seamlessly generate installation media for Pi-compatible distributions.
Many distributions aside Pi OS are supported (Ubuntu variants, Manjaro, Apertis, RISC OS,...).

Being listed & supported is very easy, with just a couple of short .json files as described here, one of which being hosted/updated on original distribution web site (hence my post here).
According to instructions, request to get listed needs to come from @ncopa I guess.

Being supported in that tool will probably drive more Pi users to Alpine distribution.
Any interest?