Add job to automate releases

[jtpio]

Fixes #805

Add a new job to the existing packaging workflow, to automate releases to PyPI and npm.

TODO

• Update RELEASE.md to mention releases are automated
• Generate the changelog using github-changelog-generator
• Create the GitHub release automatically when everything is published
• Trigger on new tags only
• Switch to the prod PyPI
• Add auth tokens as GitHub secrets
• Move the release job to its own workflow? (it's a bit tricky at the moment to share jobs and logic between github actions workflows)

[jtpio]

This might not be required if the job is moved to its own workflow and triggered with:

on:
  push:
    tags:
      - '*'

[jtpio]

To be able to get the previous tag in the following steps with git rev-list --tags

[jtpio]

Closing in favor of #805 and #913