Add initial runit support

[konimex]

(Do not merge yet, a test image will be generated in the upcoming days)

This PR is intended to add support for generating images for runit-based systems in Artix (and speed up the development for runit in Artix).

An .iso has been successfully generated, but it needs to be improved further.

Blockers:

• [x] artix-live one-shot initscript has no equivalent in runit yet (see https://github.com/artix-linux/live-services/pull/3)
• [x] can't add runit services to default runlevel yet
• [ ] runit doesn't have proper shutdown (or even booting) without manual intervention yet (binaries available, but they conflict with openrc. A solution has been proposed in the mailing list but in the meantime I'd like to make a package which is essentially just symlinks to the proper binary, which will conflict with openrc)
• TBA

[udeved]

Looks good, I would like to merge it, and we figure out shutdown stuff later, I may change something in initcpio which currently doen't work anyway when unmouting on iso shutdown..

[udeved]

initial runit support in calamares is done. https://github.com/artix-linux/calamares/commit/1d4e0bcacbbe17f6d7bf427abda3de9ec9f4128f

https://github.com/artix-linux/calamares/commit/1d4e0bcacbbe17f6d7bf427abda3de9ec9f4128f