Refactor spawner to be able to reuse code for ros2controlcli (backport #1661)

[mergify]

@christophfroehlich has mentioned that ros2 control CLI is missing the functionality to load controllers with the parameter files as we have now with the spawner. upon reviewing the code, the code would need some refactoring to reduce some duplication of code in both places and to be able also to load controllers with namespaced controller manager

This PR would be the first part of refactoring that can go along with #1562, once both the PRs are done, the ros2 control CLI can be modified to add the parameter parsing from the file and proper usage with namespacing.

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This is an automatic backport of pull request #1661 done by Mergify.

[mergify]

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Changes to be committed:
	modified:   controller_manager/controller_manager/__init__.py
	modified:   controller_manager/controller_manager/controller_manager_services.py
	modified:   controller_manager/controller_manager/hardware_spawner.py
	modified:   ros2controlcli/ros2controlcli/verb/list_controllers.py
	modified:   ros2controlcli/ros2controlcli/verb/list_hardware_components.py
	modified:   ros2controlcli/ros2controlcli/verb/list_hardware_interfaces.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   controller_manager/controller_manager/spawner.py
	both modified:   controller_manager/test/test_spawner_unspawner.cpp

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 74.07407% with 14 lines in your changes missing coverage. Please review.

Project coverage is 62.22%. Comparing base (8534e6d) to head (dd0d8e5).
Report is 1 commits behind head on iron.

Files with missing lines	Patch %	Lines
.../controller_manager/controller_manager_services.py	76.47%	7 Missing and 5 partials ⚠️
controller_manager/controller_manager/spawner.py	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             iron    #1696      +/-   ##
==========================================
- Coverage   62.24%   62.22%   -0.02%     
==========================================
  Files         112      112              
  Lines       12297    12296       -1     
  Branches     8598     8602       +4     
==========================================
- Hits         7654     7651       -3     
+ Misses        879      878       -1     
- Partials     3764     3767       +3     

Flag	Coverage Δ
unittests	62.22% <74.07%> (-0.02%)	⬇️

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

Files with missing lines	Coverage Δ
controller_manager/controller_manager/__init__.py	100.00% <ø> (ø)
...ler_manager/controller_manager/hardware_spawner.py	0.00% <ø> (ø)
controller_manager/controller_manager/spawner.py	71.07% <33.33%> (-4.39%)	⬇️
.../controller_manager/controller_manager_services.py	70.68% <76.47%> (+4.53%)	⬆️

... and 1 file with indirect coverage changes