add pythonpublish.yml

[basnijholt]

Description

Adds a Github Action script that automatically publishes to PyPI when a tag is added. This works very well with miniver.

I've been using this in https://github.com/basnijholt/adaptive-scheduler and https://github.com/basnijholt/aiokef for some time and it works very well.

Checklist

• Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• pytest passed

Type of change

Check relevant option(s).

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update