Enable initial position param in kinova xacros

The `initial_positions` parameter is already defined in the `load_arm`
and `kortex_ros2_control` macros, it is just unable to be used when
loading a kinova robot because it is not passed through in the
`load_robot` macro.

These changes add the `initial_positions` param in the `load_robot`
macro and pass it through to the `load_arm` macro so that a kinova robot
can be loaded with parameterized initial positions.

kortex_description/robots/kortex_robot.xacro

@@ -25,6 +25,7 @@
     sim_ignition:=false
     sim_isaac:=false
     use_external_cable:=false
+    initial_positions:=${dict(joint_1=0.0,joint_2=0.0,joint_3=0.0,joint_4=0.0,joint_5=0.0,joint_6=0.0,joint_7=0.0)}
     gripper_max_velocity:=100.0
     gripper_max_force:=100.0">
 
@@ -53,7 +54,8 @@
       gripper_joint_name="${gripper_joint_name}"
       gripper_max_velocity="${gripper_max_velocity}"
       gripper_max_force="${gripper_max_force}"
-      use_external_cable="${use_external_cable}">
+      use_external_cable="${use_external_cable}"
+      initial_positions="${initial_positions}">
       <xacro:insert_block name="origin" />
     </xacro:load_arm>