Standardise a path for container IO

[MarkHedleyJones]

Currently the architecture is standardised around the workspace folder.
That folder contains the project itself.
However, often applications are dealing with inputs and outputs from the host in some way and it would be good to have a standard way of linking those locations.

This could be done by having something like a switch to run like --io-path that would be mounted at a standard location inside the container (e.g. /io).