Installer nushell support

[Eternahl]

Motivation

Working Nix for nushell 🎉

Context

Closes: #9813

• Nix profiles configuration for nushell
  • [x] daemon
  • [x] user
• Nix binaries sourcing for nushell
  • [x] single-user
  • [ ] multi-user (waiting for nushell/nushell/issues/11337)
• [ ] Commands completions
• [ ] Installer tests

Using already handled shells as a template

[Nytelife26]

this should probably use modules with export-env, in much the same way starship, so that it can be imported without affecting the wider context of environment setups instead of sourced in place. other than that, lack of nushell support in the installer is the only thing preventing me from using nix on all my systems, so thank you for this :)

[stephenstubbs]

Will be so great to be able to use Nix and Nushell once this done. Any chance it can proceed now that https://github.com/nushell/nushell/issues/11337 is done?