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?

[codecov]

Codecov Report

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

Project coverage is 62.96%. Comparing base (9ce8ab3) to head (db456b9).
Report is 2 commits behind head on iron.

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             @@
##             iron    #1828      +/-   ##
==========================================
+ Coverage   62.31%   62.96%   +0.64%     
==========================================
  Files         112      113       +1     
  Lines       13137    13254     +117     
  Branches     8908     8967      +59     
==========================================
+ Hits         8186     8345     +159     
+ Misses        962      896      -66     
- Partials     3989     4013      +24     

Flag	Coverage Δ
unittests	62.96% <77.53%> (+0.64%)	⬆️

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