A better way of extracting data from containers

[mhl787156]

Currently the only way to get data out of the system is via foxglove, which we are having issues with.

Ideally we should be able to save a rosbag, or at the very least get nodes to write to a csv file or something. The problem is that the csv file is now saved within the container itself and not easily accessible to, say, plot using excel or matplotlib, matlab or whatever.

Therefore we need some standardised way of specifying the mounting of a local file in which running starling nodes can save data to and from.

Suggestion is that an example is given which mounts a local file with a node which saves data to that file. The filepath is set as an environment variable for the rosnode implementation to use.

Related to #109