Add missing `default_value` for `roofing_monotonic

resources/definitions/fdmprinter.def.json

@@ -1478,6 +1478,7 @@
                             "description": "Print top surface lines in an ordering that causes them to always overlap with adjacent lines in a single direction. This takes slightly more time to print, but makes flat surfaces look more consistent.",
                             "type": "bool",
                             "value": true,
+                            "default_value": true,
                             "enabled": "roofing_layer_count > 0 and top_layers > 0 and roofing_pattern != 'concentric'",
                             "limit_to_extruder": "roofing_extruder_nr",
                             "settable_per_mesh": true
@@ -8438,4 +8439,4 @@
             }
         }
     }
-}
+}