New opensafely clean command

We have added a command to the opensafely command line tool: opensafely clean

This command will safely remove any leftover OpenSAFELY docker artifacts from your system. Specifically, it removes old images, job containers, and file volumes that may have been created when running jobs locally on a user’s computer.

Users who have Docker runnng on WSL may find this particularly useful, as it looks like removing these leftover artifacts can help reduce memory usage.

The documentation has more information on managing your local docker resources.