feat: just return missing columns

src/elody/csv.py

@@ -188,7 +188,7 @@ def __fill_objects_from_csv(self):
             missing_columns = [x for x in self.index_mapping.values() if x not in row.keys()]
             if missing_columns:
                 raise ColumnNotFoundException(
-                    f"Not all identifying columns are present in CSV. Missing columns: {', '.join(missing_columns)}"
+                    f"{', '.join(missing_columns)}"
                 )
             lang = self.__determine_language(row)
             previous_id = None