Initial TurtleBot subscriber demo

[jleibs]

Just a fairly minimal mapping of assorted ros topics to corresponding rerun log statements.
Each message also uses tf2 to look up and log a transform for the correct point in time.

We log the point-cloud twice: once in the robot-frame and once in the map-frame as a workaround for #1522

TODO:

• ROS howto guide rerun-docs#51

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)

[teh-cmc]

This all looks great, though obviously I know nothing about ROS.

Would it be possible to put all the ROS stuff in a Dockerfile, run it in headless mode in a container and connects to from the Rerun script? That would make experimenting with this a whole lot simpler.

[jleibs]

Note from @nikolausWest : we should make sure this fails gracefully for users that don't have ROS installed since unlike the other examples the pip requirements alone are insufficient.

[nikolausWest]

Nice!