Publish to PyPi

As this is meant to be used by other libraries, it would be handy to implement an automatic pypi publishing workflow. I'm currently using the github to test the integration with affinityvae, but it will be better to use Pypi soon.

You can use the one [from the project template](https://github.com/alan-turing-institute/python-project-template/blob/main/project_template/.github/workflows/cd.yml).

Start by comparing the project-template workflow at .github/workflows/cd.yml with this repository's packaging setup. Confirm how the package is built and what credentials or publishing configuration are available. Done means an automated workflow can publish a release to PyPI for downstream libraries to install.

Written by the indexing model from the issue text.