Fix/ros2 signal and error handling

[AndreasJosefGassner]

This includes 3 fixes regarding the franka_gello_state_publisher

• Before stopping the node, we want to disable torque of the Dynamixels. For this, the publisher had implemented some signal handlers. However, those don't work in a scenario where the node is launched in a docker container and the container gets stopped. The ros2 launch system has its own signal handling, which is now used instead.
• In duo configurations, if one of the publishers exits, we now also shutdown the other one.
• When initializing the Dynamixel driver, we now catch potential connection errors and provide a meaningful error message instead of cryptic runtime errors later.