Call build_database script from a client container

Install the SEPIA backend Python package in the client image. Launch a client container to call the build_database script to initialize the database rather than executing it from the backend container.

This is the caller side of SEPIA-backend!7 (merged). Pass an additional argument -s root to the script to apply the configuration options from the corresponding section in the configuration file. Since that configuration file is present in the client container, but not in the backend, use the former to make the call.