[feature_request] Move hand collision geometries to the hand joints

[rickstaa]

In the current robot description (i.e. franka_ros v0.8.0) the collision geometries for the fingers are found inside the hand joint.

https://github.com/frankaemika/franka_ros/blob/356ec114c488c75edeaf5315633359459d37af31/franka_description/robots/hand.xacro#L30-L53

Unfortunately, third party packages like MoveIt expect each controllable joint to have a collision mesh/geometry. If these are not found, the following warnings are thrown:

[ WARN] [1628672207.286446541]: Link panda_leftfinger has visual geometry but no collision geometry. Collision geometry will be left empty. Fix your URDF file by explicitly specifying collision geometry.
[ WARN] [1628672207.286477598]: Link panda_rightfinger has visual geometry but no collision geometry. Collision geometry will be left empty. Fix your URDF file by explicitly specifying collision geometry.

This can easily be solved by moving the collision geometries from the hand joint to the finger joint. I created three possible solutions to this problem (i.e. #151, #150 or #152).

Steps to reproduce the issue

1. Clone https://github.com/rickstaa/panda_moveit_config/tree/noetic-devel-update in a catkin workspace together with the latest version of franka_ros.
2. Checkout the noetic-devel-update branch.
3. Build the catkin workspace.
4. Start the demo launch file roslaunch panda_moveit_config demo.launch.
5. See the warnings.

[rickstaa]

Will be fixed when #188 is merged.