scripts: add support for converting users from other users stores

currently we support:

- Linux/Unix users stored in shadow/passwd files
- Pure-FTPd virtual users generated using `pure-pw` CLI
- ProFTPD users generated using `ftpasswd` CLI

httpd/api_user.go

@@ -74,7 +74,6 @@ func getUserByID(w http.ResponseWriter, r *http.Request) {
 
 func addUser(w http.ResponseWriter, r *http.Request) {
 	var user dataprovider.User
-	user.PublicKeys = []string{}
 	err := render.DecodeJSON(r.Body, &user)
 	if err != nil {
 		sendAPIResponse(w, r, err, "", http.StatusBadRequest)