Use singleton approach to store and reuse the service clients (backport #1949)

[mergify]

Fixes: #1934

the node.destroy_node() at the end does the same thing by destroying clients and every subscribers, publishers etc (https://github.com/ros2/rclpy/blob/8f1f16f16090184062f1993728d063ff2680f958/rclpy/rclpy/node.py#L2017-L2053)

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This is an automatic backport of pull request #1949 done by Mergify.

[mergify]

Cherry-pick of b039baa has failed:

On branch mergify/bp/humble/pr-1949
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit b039baa.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   controller_manager/controller_manager/spawner.py

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

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]

Backport fails because #1703 hasn't been backported. @saikishor could you fix that pls?

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 62.92%. Comparing base (d7fcbca) to head (6dbd5d3).
Report is 1 commits behind head on humble.

Files with missing lines	Patch %	Lines
.../controller_manager/controller_manager_services.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1953      +/-   ##
==========================================
+ Coverage   62.87%   62.92%   +0.05%     
==========================================
  Files         109      109              
  Lines       12494    12505      +11     
  Branches     8481     8479       -2     
==========================================
+ Hits         7855     7869      +14     
+ Misses        854      852       -2     
+ Partials     3785     3784       -1     

Flag	Coverage Δ
unittests	62.92% <93.33%> (+0.05%)	⬆️

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/spawner.py	70.07% <100.00%> (+0.22%)	⬆️
.../controller_manager/controller_manager_services.py	82.92% <92.85%> (+1.10%)	⬆️

... and 1 file with indirect coverage changes

[christophfroehlich]

The namespacing support "silently" is added now?

[saikishor]

The namespacing support "silently" is added now?

Yes! It always existed in the name of the argument, but with this even the cli should be happy. Moreover, this only applies if the service is relative and not absolute

If you prefer, not to have it. I can fix it