feat: implement method to start a game

src/main/java/uulm/teamname/marvelous/gamelibrary/gamelogic/GameInstance.java

@@ -57,6 +57,13 @@ public class GameInstance {
         return manager.processRequests(requests, false);
     }
 
+    /**
+     * Initializes and starts the game.
+     */
+    public void startGame() {
+        emit(manager.startGame());
+    }
+
     /**
      * Produces a {@link EventType#GamestateEvent} for the current {@link GameState}.
      * @return The resulting event