Doesn't copy `authorized_keys` from `/etc/ssh/authorized_keys.d/${sshUser}`

My custom installer ISO has authorized keys for the `nixos` user set via `users.users.nixos.openssh.authorizedKeys.keys` but none for `root`. In such cases it would be helpful if `nixos-anywhere` would additionally try to copy over the `authorized_keys` file from `/etc/ssh/authorized_keys.d/$USER`. https://github.com/nix-community/nixos-anywhere/blob/e86fad431cf9161ca39747972bd255897572dc3b/src/nixos-anywhere.sh#L1030-L1036