Add a command to print out templated or other regular files from within the container

[thomas-anderson-bsl]

We currently have a launcher and install command that print out templated files.
In one of our applications, we also need to cat out a file from within the container.

We should try to consolidate these into a single way to extract files (templated or not) from the container.

[thomas-anderson-bsl]

This can now be achieved through custom commands which can run docker exec commands on running containers