Create docker_setup.md

[DonRichards]

Issue #814 - Add Dockerfile docs.
PR #815 - Addressing compatibility and remove DOCKER_BUILDKIT in the Docker setup

What does this PR do?

This PR adds a new file detailing the process of setting up and using the Dockerfile for running Islandora Workbench in a container. It covers building the Docker image, running the container, handling permissions, mounting directories outside of the workbench directory, and configurations specific to Docker environments.

What changes were made?

• Added docs/docker_setup.md to provide step-by-step instructions for:
• Building the Docker image.
• Running the Docker container with appropriate volume mounts and network settings.
• Managing file permissions and resolving common issues such as permission errors.
• Explaining the use of DOCKER_BUILDKIT=0 for compatibility reasons.