Add log level support to spawner node

[bijoua29]

Want to be able to control the output from the spawner node. This PR adds a log-level argument that is set on the spawner node.

[codecov-commenter]

Codecov Report

Merging #972 (1bc0344) into master (925f5f3) will decrease coverage by 1.85%.
The diff coverage is 35.84%.

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@@            Coverage Diff             @@
##           master     #972      +/-   ##
==========================================
- Coverage   34.61%   32.77%   -1.85%     
==========================================
  Files          52       91      +39     
  Lines        2981     9511    +6530     
  Branches     1855     6408    +4553     
==========================================
+ Hits         1032     3117    +2085     
- Misses        310      676     +366     
- Partials     1639     5718    +4079     

Flag	Coverage Δ
unittests	32.77% <35.84%> (-1.85%)	⬇️

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

Impacted Files	Coverage Δ
controller_manager/src/controller_manager.cpp	38.41% <ø> (-1.30%)	⬇️
controller_manager/src/ros2_control_node.cpp	0.00% <0.00%> (ø)
..._interface/include/hardware_interface/actuator.hpp	100.00% <ø> (ø)
...re_interface/include/hardware_interface/sensor.hpp	100.00% <ø> (ø)
...re_interface/include/hardware_interface/system.hpp	100.00% <ø> (ø)
hardware_interface/src/resource_manager.cpp	50.00% <ø> (-3.63%)	⬇️
hardware_interface/src/sensor.cpp	50.52% <ø> (ø)
hardware_interface/src/system.cpp	55.45% <ø> (ø)
...rface/test/mock_components/test_generic_system.cpp	9.14% <ø> (ø)
...dware_interface/test/test_component_interfaces.cpp	32.44% <ø> (+4.25%)	⬆️
... and 69 more

... and 18 files with indirect coverage changes

[bmagyar]

Thanks! Very clean!

[destogl]

Looking great! Moreover, great solution for redirecting output of the load_parameter_file function.