PyPI publishing
This MR
- changes the version to a "development release", indicating not-yet-even-alpha status
- enables publishing the built package to PyPI
The required environment variable POETRY_PYPI_TOKEN_PYPI has already be set in this GitLab project's CI/CD settings to an API token created for the geometalab PyPI account at https://pypi.org/manage/account/#api-tokens
/cc @fhauser