Improve Nushell adoption by automatically integrating completions via nu_scripts

[shikanime]

Description

Nushell is still largely a small player, but it would be handy if most of the modules in the home manager repository had autocompletion similar to zsh, fish and bash. Most programs don't support nushell natively, but it would be interesting to use nu_scripts as an alternative, as it is a community driven but official set of scripts.

I'd like to work on this if this request seems pertinent, as it will use a third party autocompletion scripts. Or it would be better to look into it on the nixpkgs side.