`fh add` Adding a url to inputs that ist not a flake should add `flake = false;`

Adding a input url `fh add github:emacs-straight/org-mode` that is not a flake only adds `org-mode.url = "github:emacs-straight/org-mode";`. 
The tool should detect that the input is not a flake or there should be an option to also add `org-mode.flake = false;` for this input.