Figure out how to use a position or velocity-based controller with Gazebo and our arm

[Roozki]

We can use the old URDF for now, but Gazebo does not seem to work when using a position-based controller. We need a position or velocity based controller for realtime servo jogging (if we use the moveit_servo pkg). Our actual arm seems to like velocity-based control, so a velocity-based simulation would be preferred. Ideally, we would be able to change the controllers on-the-fly with our arm between effort, position and velocity. Currently we have only gotten the effort controllers to work in Gazebo.

Gazebo version: 11.x -> this is the recommended gazebo_classic version to use with ROS1 noetic, as well as ROS2 foxy. We have had much more luck with gazebo_classic compared to the newer versions.