Access data in worker

Mount $HOST_DIRECTORY/data to /app/data in the container so it can be accessed by ingestion and scoring programs.

This can be used to store data directly inside the compute workers.

See:

• #874 (closed)

Review:

• Tested and it work
• CircleCI tests are passing
• Documentation is updated

Next steps:

• Merge PR
• Update docker images (cpu and gpu)