Install Gazebo as part of Tutorials image build

[sea-bass]

Description

There have been issues building the tutorials image because now some of the packages (namely Robotiq and ros2_kortex) depend on Gazebo being installed.

This will work for Jazzy/Rolling, but I think there need to be args introduced to make this work on other distros (or even changing gz for ignition)

So you will then need to pass in this GZ_VERSION arg in the moveit2 CI job here: https://github.com/moveit/moveit2/blob/1d93035fc4fbc2831916bce26d7b03e15b8a86d5/.github/workflows/tutorial_docker.yaml#L19

NOTE: You should see the effects of this in the post-merge action for this PR. I've also dispatched the workflow so you can see it on this branch: https://github.com/moveit/moveit2_tutorials/actions/runs/10207096230

(all previous failing runs can be found here: https://github.com/moveit/moveit2_tutorials/actions/workflows/docker.yml)

Checklist

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[sea-bass]

An alternative to all this, btw, is to remove the dependency on ros_gz_sim from the ros2_kortex package... while that wouldn't be "proper", as it factually depends on Gazebo, you could consider it an optional dependency given it's just an option in some of the xacros.

[sjahr]

Thanks for fixing this. I think for now this is a good way forward