Clean up docker helper for loading

From issue #65

The Dockerfile is designed to be built by:

https://github.com/ai-cfia/ailab-db/blob/main/bin/build-dataloader.sh

and run with the help of these scripts in bin/ such as:

https://github.com/ai-cfia/ailab-db/blob/main/bin/load-data-container.sh

where a volume containing the schema and data dump is provided to mount on /data; volume created from:

https://github.com/ai-cfia/ailab-db/blob/main/bin/build-data-volume.sh

* this could be made clearer by moving the Dockerfile to bin/ and adding a comment at the top of the Dockerfile explaining how it is used

* ensure that we have a test making sure this flows work on a sample schema.sql and small dataset within the continuous build.

_Originally posted by @rngadam in https://github.com/ai-cfia/ailab-db/issues/65#issuecomment-1832326825_