Map a datastore directory in the Docker image

[neilenns]

Fixes #191

Description of changes

• Creates a www folder in /node-deepstackai-trigger for use in the future as a storage location for annotated images.
• Update the Dockerfile to generate a final image with the mount point pre-defined with the right user permissions
• Update the sample docker-compose.yaml file to include the volume mount
• Update the .devcontainer configuration to pre-define the folder and mount a volume

Checklist

If your change touches anything under src or the README.md file
these items must be done:

• User-facing change description added to unreleased section of CHANGELOG.md