Automatic linting with CI with black

[htwangtw]

Detailed Description

At the July dev call, @smoia mentioned wanting to add linting with CI on PRs for #402

Context / Motivation

We want a more consistent code style, not loading style issue on the project owner, and minimise barriers (ancillary issues such as complex dev environment setup) for new contributors. Everyone wins if there's a lazy linter built into CI.

Possible Implementation

Lint Action supports such a feature. However, it's unclear regarding known conflicts with isort/flake8.
I found another solution using the create-pull-request GitHub action.
This solution is buried at the very end of the guide on market place:
https://github.com/marketplace/actions/run-black-formatter

I am happy to test out and do a PR. Can also check how to integrate isort in the same GitHub action.
Any other style-related stuff you want to add to the GitHub action?

[smoia]

Just realised this was closed by #445!