Feat: Make start and end of a labyrinth configurable.

Also, small refactoring.

src/main/resources/labyrinth.schema.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://manuel.friedli.info/labyrinth-1/labyrinth.schema.json",
+  "$id": "https://manuel.friedli.info/labyrinth-2/labyrinth.schema.json",
   "javaType": "ch.fritteli.labyrinth.generator.json.JsonLabyrinth",
   "type": "object",
   "additionalProperties": false,
@@ -8,6 +8,8 @@
     "id",
     "width",
     "height",
+    "start",
+    "end",
     "grid"
   ],
   "properties": {
@@ -23,6 +25,12 @@
       "type": "integer",
       "minimum": 1
     },
+    "start": {
+      "$ref": "#/$defs/coordinates"
+    },
+    "end": {
+      "$ref": "#/$defs/coordinates"
+    },
     "grid": {
       "$ref": "#/$defs/grid"
     }
@@ -64,6 +72,25 @@
           "type": "boolean"
         }
       }
+    },
+    "coordinates": {
+      "type": "object",
+      "javaType": "ch.fritteli.labyrinth.generator.json.JsonCoordinates",
+      "additionalProperties": false,
+      "required": [
+        "x",
+        "y"
+      ],
+      "properties": {
+        "x": {
+          "type": "integer",
+          "minimum": 0
+        },
+        "y": {
+          "type": "integer",
+          "minimum": 0
+        }
+      }
     }
   }
 }