Use launch_utils instead of a spawner per controller (backport #666)

[mergify]

Adressing #640, maybe this fixes the flakyness.

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This is an automatic backport of pull request #666 done by Mergify.

[mergify]

Cherry-pick of ceed8cf has failed:

On branch mergify/bp/humble/pr-666
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit ceed8cf.
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  (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:   example_13/CMakeLists.txt
	modified:   example_13/package.xml
	modified:   example_13/test/test_three_robots_launch.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   example_13/bringup/launch/three_robots.launch.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