Add single extruder definition for Ender-3.

resources/definitions/creality_ender3.def.json

@@ -8,7 +8,10 @@
         "manufacturer": "Creality3D",
         "file_formats": "text/x-gcode",
         "platform": "creality_ender3_platform.stl",
-        "preferred_quality_type": "draft"
+        "preferred_quality_type": "draft",
+        "machine_extruder_trains": {
+            "0": "creality_ender3_extruder_0"
+        }
     },
     "overrides": {
         "machine_name": {
@@ -37,9 +40,6 @@
                 [30, 34]
             ]
         },
-        "material_diameter": {
-            "default_value": 1.75
-        },
         "acceleration_enabled": {
             "default_value": true
         },

resources/extruders/creality_ender3_extruder_0.def.json

@@ -0,0 +1,22 @@
+{
+    "id": "creality_ender3_extruder_0",
+    "version": 2,
+    "name": "Extruder 1",
+    "inherits": "fdmextruder",
+    "metadata": {
+        "machine": "creality_ender3",
+        "position": "0"
+    },
+
+    "overrides": {
+        "extruder_nr": {
+            "default_value": 0
+        },
+        "machine_nozzle_size": {
+            "default_value": 0.4
+        },
+        "material_diameter": {
+            "default_value": 1.75
+        }
+    }
+}