Update space_robots demo to match the new build approach

[xfiderek]

See discussion https://github.com/space-ros/space-ros/discussions/140 and issue https://github.com/space-ros/space-ros/issues/107 for more context

TODOs

• Move dockerfile to demos repo
• Use a new generate_repos.sh file from updated spaceros dev image and generate pinned .repos file

[mkhansenbot]

I think space_robots will also really be moveit2_demo or just a /docker folder in the canadarm demo?