Add `COSMIC` as a desktop option

[yarons]

https://github.com/pop-os/cosmic-epoch

https://wiki.archlinux.org/title/COSMIC

Written in Rust, looks pretty promising.

[omentic]

COSMIS is pre-alpha. Once a stable (or anything but alpha) release is made, it'll get packaged pretty fast and we can add it as an option. For now, it's a non-starter, cause that's probably several years away.

[killertofus]

it's out now https://archlinux.org/groups/x86_64/cosmic/

[Torxed]

Thank you @killertofus for the PR, I requested some minor changes - after which I can merge and it will be joining the next release :)