Add support for 1.20.3

src/config.json

@@ -105,6 +105,11 @@
       "id": "1.20.2",
       "ref": "1.20.2",
       "pack_format": 18
+    },
+    {
+      "id": "1.20.3",
+      "ref": "1.20.3",
+      "pack_format": 26
     }
   ],
   "generators": [