[JTC] Disable use of closed-loop PID adapter if controller is used in open-loop mode. (backport #551)

[mergify]

This is an automatic backport of pull request #551 done by Mergify.
Cherry-pick of 8029a2f has failed:

On branch mergify/bp/humble/pr-551
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Changes to be committed:
	modified:   joint_trajectory_controller/src/joint_trajectory_controller.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   joint_trajectory_controller/doc/userdoc.rst

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

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