Set default camera angle in cart_pole example (#3159)

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

Author: scpeters

examples/scripts/reinforcement_learning/simple_cart_pole/cart_pole.sdf

@@ -23,6 +23,22 @@
       name="gz::sim::systems::SceneBroadcaster">
     </plugin>
 
+    <gui fullscreen="0">
+      <plugin filename="MinimalScene" name="3D View">
+        <gz-gui>
+          <title>3D View</title>
+          <property type="bool" key="showTitleBar">false</property>
+          <property type="string" key="state">docked</property>
+        </gz-gui>
+        <engine>ogre2</engine>
+        <scene>scene</scene>
+        <ambient_light>0.4 0.4 0.4</ambient_light>
+        <background_color>0.8 0.8 0.8</background_color>
+        <!-- set default user camera pose -->
+        <camera_pose>0 6 3 0 0 -1.57</camera_pose>
+      </plugin>
+    </gui>
+
     <light type="directional" name="sun">
       <cast_shadows>true</cast_shadows>
       <pose>0 0 10 0 0 0</pose>