[ros2_control_node] add thread_priority option to the ros2_control_node (backport #1820)

[mergify]

Right now, the thread_priority is hard-coded to 50, this PR allows the users to be able to choose their desired priority by setting a parameter at launch time

ros2_control/controller_manager/src/ros2_control_node.cpp

Line 32 in b0da4a1

int const kSchedPriority = 50;

---

This is an automatic backport of pull request #1820 done by Mergify.

[mergify]

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	both modified:   controller_manager/src/ros2_control_node.cpp
	both modified:   doc/release_notes.rst

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 62.41%. Comparing base (7ca9d7f) to head (9a4ee8d).
Report is 1 commits behind head on iron.

Files with missing lines	Patch %	Lines
controller_manager/src/ros2_control_node.cpp	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             iron    #1825      +/-   ##
==========================================
+ Coverage   62.38%   62.41%   +0.02%     
==========================================
  Files         112      112              
  Lines       12967    12969       +2     
  Branches     8768     8770       +2     
==========================================
+ Hits         8090     8095       +5     
+ Misses        952      948       -4     
- Partials     3925     3926       +1     

Flag	Coverage Δ
unittests	62.41% <50.00%> (+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/src/ros2_control_node.cpp	80.00% <50.00%> (+1.21%)	⬆️

... and 2 files with indirect coverage changes