feat: add completion for chezmoi

[AtifChy]

This PR add completion for chezmoi.

Generated using AI with some tweaks from me.

[fdncred]

Can you add a readme.md in the new folder to explain what chezmoi is and where to find it?

[Paul-16098]

def "nu-complete managed" [] {
  {
    options: {
      completion_algorithm: substring
    }
    completions: ((chezmoi managed) | lines | par-each --keep-order { "~/" + ($in) })
  }
}
def "nu-complete unmanaged" [] {
  {
    options: {
      completion_algorithm: substring
    }
    completions: ((chezmoi unmanaged) | lines | par-each --keep-order { "~/" + ($in) })
  }
}

in chezmoi apply add ...target: path@"nu-complete managed"
in chezmoi forget add ...target: path@"nu-complete managed"