set multiple obstacles from area

added a parameter to GridArea to control how many obstacles will be created in the scene

Project/Assets/ML-Agents/Examples/GridWorld/Scenes/GridWorld.unity

   m_ReflectionIntensity: 1
   m_CustomReflection: {fileID: 0}
   m_Sun: {fileID: 0}
-  m_IndirectSpecularColor: {r: 0.44971168, g: 0.4997775, b: 0.57563686, a: 1}
+  m_IndirectSpecularColor: {r: 0.44971228, g: 0.49977815, b: 0.57563734, a: 1}
   m_UseRadianceAmbientProbe: 0
 --- !u!157 &3
 LightmapSettings:
   agentParameters:
     maxStep: 100
   hasUpgradedFromAgentParameters: 1
-  maxStep: 100
+  MaxStep: 100
   area: {fileID: 1795599557}
   timeBetweenDecisionsAtInference: 0.15
   renderCamera: {fileID: 797520692}
   m_Name: 
   m_EditorClassIdentifier: 
   m_BrainParameters:
-    vectorObservationSize: 0
-    numStackedVectorObservations: 1
-    vectorActionSize: 05000000
-    vectorActionDescriptions: []
-    vectorActionSpaceType: 0
+    VectorObservationSize: 0
+    NumStackedVectorObservations: 1
+    VectorActionSize: 05000000
+    VectorActionDescriptions: []
+    VectorActionSpaceType: 0
   m_Model: {fileID: 11400000, guid: a812f1ce7763a4a0c912717f3594fe20, type: 3}
   m_InferenceDevice: 0
   m_BehaviorType: 0
+  m_UseChildActuators: 1
+  m_ObservableAttributeHandling: 0
 --- !u!114 &125487791
 MonoBehaviour:
   m_ObjectHideFlags: 0
   m_RenderTexture: {fileID: 8400000, guid: 114608d5384404f89bff4b6f88432958, type: 2}
   m_SensorName: RenderTextureSensor
   m_Grayscale: 0
+  m_ObservationStacks: 1
   m_Compression: 1
 --- !u!1 &260425459
 GameObject:
   trueAgent: {fileID: 125487785}
   goalPref: {fileID: 1508142483324970, guid: 1ec4e4e96e7514d45b7ebc3ba5a9a481, type: 3}
   pitPref: {fileID: 1811317785436014, guid: d13ee2db77b3a4dcc8664d2fe2a0f219, type: 3}
+  numberOfObstacles: 2
 --- !u!4 &1795599558
 Transform:
   m_ObjectHideFlags: 0

Project/Assets/ML-Agents/Examples/GridWorld/Scripts/GridArea.cs

     public GameObject goalPref;
     public GameObject pitPref;
     GameObject[] m_Objects;
+    public int numberOfObstacles = 1;
 
     GameObject m_Plane;
     GameObject m_Sn;
         transform.position = m_InitialPosition * (m_ResetParams.GetWithDefault("gridSize", 5f) + 1);
         var playersList = new List<int>();
 
-        for (var i = 0; i < (int)m_ResetParams.GetWithDefault("numObstacles", 1); i++)
+        for (var i = 0; i < (int)m_ResetParams.GetWithDefault("numObstacles", numberOfObstacles); i++)
         {
             playersList.Add(1);
         }