fix: fix dual panda motion generator PID gains not found bug

This commit makes sure that the 'arm_id' is taken into account when the
motion generator PID gains are loaded onto the ROS parameter server.

CHANGELOG.md

@@ -6,6 +6,7 @@
   * `franka_example_controllers`: Extend the `teleop_joint_pd_example_controller` with joint walls to actively avoid position or velocity limit violations.
   * `franka_control`: Configurable `arm_id` in launch & config files
   * `franka_description`: URDF now contains `$(arm_id)_linkN_sc` links containing the capsule collision modules used for self-collision avoidance (MoveIt).
+  * `franka_gazebo`: Fix motion generator config respects `arm_id`
 
 ## 0.9.0 - 2022-03-29
 

franka_gazebo/config/franka_hw_sim.yaml

@@ -16,19 +16,19 @@ franka_gripper:
 motion_generators:
   position:
     gains:
-      panda_joint1: { p: 600, d: 30, i: 0 }
-      panda_joint2: { p: 600, d: 30, i: 0 }
-      panda_joint3: { p: 600, d: 30, i: 0 }
-      panda_joint4: { p: 600, d: 30, i: 0 }
-      panda_joint5: { p: 250, d: 10, i: 0 }
-      panda_joint6: { p: 150, d: 10, i: 0 }
-      panda_joint7: { p:  50, d:  5, i: 0 }
+      $(arg arm_id)_joint1: { p: 600, d: 30, i: 0 }
+      $(arg arm_id)_joint2: { p: 600, d: 30, i: 0 }
+      $(arg arm_id)_joint3: { p: 600, d: 30, i: 0 }
+      $(arg arm_id)_joint4: { p: 600, d: 30, i: 0 }
+      $(arg arm_id)_joint5: { p: 250, d: 10, i: 0 }
+      $(arg arm_id)_joint6: { p: 150, d: 10, i: 0 }
+      $(arg arm_id)_joint7: { p:  50, d:  5, i: 0 }
   velocity:
     gains:
-      panda_joint1: { p: 30, d: 0, i: 0 }
-      panda_joint2: { p: 30, d: 0, i: 0 }
-      panda_joint3: { p: 30, d: 0, i: 0 }
-      panda_joint4: { p: 30, d: 0, i: 0 }
-      panda_joint5: { p: 10, d: 0, i: 0 }
-      panda_joint6: { p: 10, d: 0, i: 0 }
-      panda_joint7: { p:  5, d:  0, i: 0 }
+      $(arg arm_id)_joint1: { p: 30, d: 0, i: 0 }
+      $(arg arm_id)_joint2: { p: 30, d: 0, i: 0 }
+      $(arg arm_id)_joint3: { p: 30, d: 0, i: 0 }
+      $(arg arm_id)_joint4: { p: 30, d: 0, i: 0 }
+      $(arg arm_id)_joint5: { p: 10, d: 0, i: 0 }
+      $(arg arm_id)_joint6: { p: 10, d: 0, i: 0 }
+      $(arg arm_id)_joint7: { p:  5, d:  0, i: 0 }