Create named volume for available digest data

[alyssadai]

One option could be to create a named QPN volume ahead of time, and then either manually mount it every time the container starts - or to just add a docker-compose file for this one container and define the volume in there.

Originally posted by @surchs in #150 (comment)

Example:

# get QPN data
git clone https://github.com/neurodatascience/nipoppy-qpn.git
# Make (initially empty QPN volume)
docker volume create qpn_data
# use silly-container just to copy data into the volume
docker run --rm -v qpn_data:/target -v $(PWD)/nipoppy-qpn:/source alpine cp -a /source/. /target/
# Use the volume as read-only access
docker run -d -p 8050:8050 -v qpn_data:/app/nipoppy-qpn neurobagel/digest:nightly

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