Forward trajectory controller (backport #944)

[mergify]

The controller should be able to forward a cartesian tracjectory to the robot for interpolation.
Creates errors on compilation due to multiple definition of functions, when inheriting from the joint_trajectory_controller. But looking at the passthrough controllers from ROS1 that may not be the right controller to use anyway?
All inputs are welcome.

closes #839

---

This is an automatic backport of pull request #944 done by Mergify.

[mergify]

Cherry-pick of ca5fb3e has failed:

On branch mergify/bp/iron/pr-944
Your branch is up to date with 'origin/iron'.

You are currently cherry-picking commit ca5fb3e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   ur_controllers/CMakeLists.txt
	modified:   ur_controllers/controller_plugins.xml
	modified:   ur_controllers/doc/index.rst
	new file:   ur_controllers/include/ur_controllers/passthrough_trajectory_controller.hpp
	modified:   ur_controllers/package.xml
	new file:   ur_controllers/src/passthrough_trajectory_controller.cpp
	new file:   ur_controllers/src/passthrough_trajectory_controller_parameters.yaml
	modified:   ur_robot_driver/CMakeLists.txt
	modified:   ur_robot_driver/config/ur_controllers.yaml
	modified:   ur_robot_driver/include/ur_robot_driver/hardware_interface.hpp
	modified:   ur_robot_driver/launch/ur10.launch.py
	modified:   ur_robot_driver/launch/ur10e.launch.py
	modified:   ur_robot_driver/launch/ur16e.launch.py
	modified:   ur_robot_driver/launch/ur20.launch.py
	modified:   ur_robot_driver/launch/ur3.launch.py
	modified:   ur_robot_driver/launch/ur30.launch.py
	modified:   ur_robot_driver/launch/ur3e.launch.py
	modified:   ur_robot_driver/launch/ur5.launch.py
	modified:   ur_robot_driver/launch/ur5e.launch.py
	modified:   ur_robot_driver/src/hardware_interface.cpp
	new file:   ur_robot_driver/test/integration_test_controller_switch.py
	modified:   ur_robot_driver/test/robot_driver.py
	modified:   ur_robot_driver/test/test_common.py

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   ur_robot_driver/launch/ur_control.launch.py
	deleted by us:   ur_robot_driver/scripts/example_move.py
	deleted by us:   ur_robot_driver/urdf/ur.ros2_control.xacro

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[urfeex]

This feature will not land in iron anymore.