Start executing passthrough trajectories earlier than all points are transferred. (backport #1313)

[mergify]

When transferring trajectories with many waypoints it can take quite a
while until all points are transferred from the controller to the
hardware interface, especially on lower hardware_interface update rates.

With this change, execution starts as soon as enough trajectory points
are transferred to fill 5 control cycles.

This PR effectively allows reducing the hardware_interface update_rate
when using the passthrough_trajectory_controller significantly. This
will reduce the networking requirements improving the overall user
experience.

---

This is an automatic backport of pull request #1313 done by Mergify.

[mergify]

Cherry-pick of 14f80ac has failed:

On branch mergify/bp/humble/pr-1313
Your branch is up to date with 'origin/humble'.

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Changes to be committed:
	modified:   ur_controllers/include/ur_controllers/passthrough_trajectory_controller.hpp
	modified:   ur_robot_driver/include/ur_robot_driver/hardware_interface.hpp
	modified:   ur_robot_driver/src/hardware_interface.cpp

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   ur_controllers/src/passthrough_trajectory_controller.cpp
	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