Launch file for running gzserver

[caguero]

🎉 New feature

Summary

This patch allows to run gzserver as an executable or as a composable node.

How to test it?

Use the provided gz_server.launch.py to run gzserver as an executable:

ros2 launch ros_gz_sim gz_server.launch.py world_sdf_file:=empty.sdf

Confirm that you see gzserver loading and verify that no container has been created:

caguero@cold:~/ros_gz_ws$ ros2 component list

Now CTRL-C gzserver and try the composable version:

ros2 launch ros_gz_sim gz_server.launch.py world_sdf_file:=empty.sdf use_composition:=True

Confirm that you see gzserver loading and verify that a new container has been created:

caguero@cold:~/ros_gz_ws$ ros2 component list
/ros_gz_container
  1  /gzserver

Test it

Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.