Add flake8 job to the github actions

[jomey]

Just talked to Weji and he recommended Ruff https://docs.astral.sh/ruff/

[lsetiawan]

Instead of simply running style checks within github actions, it is now recommended to have a pre-commit instead that runs before any code changes is committed. Once pre-commit is setup, you can setup pre-commit.ci integration so that PR from outside contributors also get a style check. As @jomey referenced above, ruff will work with pre-commit.. simply add a hook to it.