Allow importing velocity command from mcap files

[pvandervelde]

This allows us to match simulated outputs to outputs from real robots. This should help investigate issues.

[pvandervelde]

There are a number of issues with this:

• Mcap / rosbag often contain a decent number of velocity commands. So far we have only tested with some simple sets with maybe 200 steps. Given that each step takes a few seconds this means that running a mcap/rosbag file would take a very long time (multiple hours)
• The simulation code assumes that every end state is reachable and that it is reached at the end of the command. However in real life this isn't the case and so velocity commands are often send as a stream. In this case the motors don't necessarily reach the commanded velocities at the end of the time step. The simulation doesn't handle this at the moment so just reading in the velocity commands would lead to something odd.