Add a build system spec file

[tanius]

This import script requires specific versions of libraries it depends on (details). In the current installation instructions, this is managed with this installation command:

pip install "neo4j~=5.0" psycopg2-binary

For easier installation, esp. if other version dependencies emerge in the future, it would be a good idea to use a pyproject.toml build system interface file, allowing pip to automatically pick up the correct versions.

That change could require other changes first (different versions of Python and pip).