[Spawner] Allow arguments per controller instead of global args (backport #2895)

[mergify]

This PR adds some changes to the Spawner to allow it to define the controller args per controller rather than global args for all the controllers.

I've added a new function in the launch_utils and I tested it using the following changes in example_12
https://github.com/ros-controls/ros2_control_demos/blob/advanced_spawner/example_12/bringup/launch/rrbot.launch.py

With this change we can do both the following

ros2 run controller_manager spawner ctrl_1 ctrl_2 --inactive --controller-ros-args ....

and

ros2 run controller_manager spawner --controller ctrl_1 --load-only --controller ctrl_2 --inactive --controller-ros-args ...

---

This is an automatic backport of pull request #2895 done by Mergify.

[codecov]

Codecov Report

❌ Patch coverage is 82.01439% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.25%. Comparing base (94a432f) to head (ed23a38).
⚠️ Report is 2 commits behind head on kilted.

Files with missing lines	Patch %	Lines
...troller_manager/controller_manager/launch_utils.py	2.56%	38 Missing ⚠️
controller_manager/controller_manager/spawner.py	78.70%	15 Missing and 8 partials ⚠️
controller_manager/test/test_advanced_spawner.cpp	94.81%	0 Missing and 14 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           kilted    #3053      +/-   ##
==========================================
- Coverage   89.36%   89.25%   -0.12%     
==========================================
  Files         157      158       +1     
  Lines       18792    19170     +378     
  Branches     1510     1549      +39     
==========================================
+ Hits        16794    17110     +316     
- Misses       1377     1424      +47     
- Partials      621      636      +15     

Flag	Coverage Δ
unittests	89.25% <82.01%> (-0.12%)	⬇️

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

Files with missing lines	Coverage Δ
controller_manager/test/test_advanced_spawner.cpp	94.81% <94.81%> (ø)
controller_manager/controller_manager/spawner.py	72.76% <78.70%> (+2.35%)	⬆️
...troller_manager/controller_manager/launch_utils.py	22.97% <2.56%> (-22.75%)	⬇️

... and 1 file with indirect coverage changes

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[christophfroehlich]

#3054