add support for override-input

### Prerequisites - [x] I have searched existing issues to make sure this isn't a duplicate - [x] I have checked the documentation to see if this feature already exists ### Problem Description nix \ --extra-experimental-features "nix-command flakes" \ run github:nix-community/nixos-anywhere -- \ -i ~/.ssh/id_ed25519 \ --flake "path:${ROOT}#i" \ --override-input host path:$ROOT/nix/vps/conf/$HOST.nix \ "root@${HOST}" ### Proposed Solution I can use override-input for dynamic vps config ### Alternatives Considered _No response_ ### Feature Type New command-line option ### Use Case _No response_ ### Implementation Ideas _No response_ ### Additional Context _No response_