Installer nushell support

[Eternahl]

Motivation

Working Nix for nushell 🎉

Context

Closes: #9813

• Nix profiles configuration for nushell
  • daemon
  • user
• Nix binaries sourcing for nushell
  • single-user
  • multi-user (waiting for Enable system package manager to install modules such as completions in system managed paths nushell/nushell#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 :)