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]

Cherry-pick of 5dbd6d5 has failed:

On branch mergify/bp/humble/pr-1759
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 5dbd6d5.
  (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:   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

[codecov]

Codecov Report

Attention: Patch coverage is 77.53623% with 31 lines in your changes missing coverage. Please review.

Project coverage is 63.15%. Comparing base (0cb0716) to head (465bb9e).
Report is 1 commits behind head on humble.

Files with missing lines	Patch %	Lines
controller_manager/test/test_hardware_spawner.cpp	78.81%	7 Missing and 18 partials ⚠️
...ler_manager/controller_manager/hardware_spawner.py	70.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1827      +/-   ##
==========================================
+ Coverage   62.47%   63.15%   +0.67%     
==========================================
  Files         108      109       +1     
  Lines       12169    12286     +117     
  Branches     8257     8310      +53     
==========================================
+ Hits         7603     7759     +156     
+ Misses        884      822      -62     
- Partials     3682     3705      +23     

Flag	Coverage Δ
unittests	63.15% <77.53%> (+0.67%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ler_manager/controller_manager/hardware_spawner.py	70.23% <70.00%> (+70.23%)	⬆️
controller_manager/test/test_hardware_spawner.cpp	78.81% <78.81%> (ø)

... and 2 files with indirect coverage changes

[christophfroehlich]

Thx @saikishor for fixing