Fix Hardware spawner and add tests for it (backport #1759)

[mergify]

This basically implements my comments from #1682 (review)

I discussed with @destogl that I would create a new PR including his commit from #1682. So, this effectively replaces #1682.

It basically changes the following things:

• Actually makes the hardware spawner work. I think it never worked correctly the way it was structured before. (is_hardware_component_loaded checks for one single string, while activate_components and configure_components expect a list.)
• Fully implement that the hardware spawner allows specifying a list of components that should be started. This is cmdline-interface-breaking (basically only on a parameter description level) change but since it never worked I would expect nobody has been using it so far, so we can safely backport it.
• Add tests for hardware_spawner (mainly implemented by @destogl)

  ---

  This is an automatic backport of pull request Fix Hardware spawner and add tests for it #1759 done by Mergify.

[mergify]

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Changes to be committed:
	modified:   controller_manager/controller_manager/hardware_spawner.py
	modified:   controller_manager/doc/userdoc.rst
	new file:   controller_manager/test/test_hardware_spawner.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   controller_manager/CMakeLists.txt

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

[christophfroehlich]

@fmauch could you maybe have a look why the test fail on humble?