Can no longer use --show-trace with #activate

[GGORG0]

Hi, previously, with the Nix version of #activate, we were able to provide custom arguments to the function that would be passed on to nixos-rebuild, such as --show-trace. Now, with the Nushell version this is not possible.

Edit: related to #57

[srid]

It is a regression from Nushell rewrite of the activate script which was done to add some features; #56, #60

More generally, we should make the new activate script take arbitrary arguments from the user and pass them nixos-rebuild, darwin-rebuild or home-manager switch as appropriate.