Add missing output port for angular distance traveled in Spin action (#60)

Author: RBT22

nav2_behavior_tree/nav2_tree_nodes.xml

@@ -194,6 +194,7 @@
       <input_port name="time_allowance">Allowed time for spinning</input_port>
       <input_port name="server_name">Server name</input_port>
       <input_port name="server_timeout">Server timeout</input_port>
+      <output_port name="angular_distance_traveled">Angular distance traveled (may be less than requested)</output_port>
       <output_port name="error_code_id">Spin error code</output_port>
     </Action>