proper log for registering guests

src/model/usertrip.rs

@@ -11,7 +11,7 @@ impl UserTrip {
         user: &User,
         trip_details: &TripDetails,
         user_note: Option<String>,
-    ) -> Result<(), UserTripError> {
+    ) -> Result<String, UserTripError> {
         if trip_details.is_full(db).await {
             return Err(UserTripError::EventAlreadyFull);
         }
@@ -81,7 +81,7 @@ impl UserTrip {
             .await;
         }
 
-        Ok(())
+        Ok(name_newly_registered_person)
     }
 
     pub async fn delete(