Add base black and isort configuration

[legoktm]

black and isort are effectively a pair, both do code (re)formatting.

This defines the following Makefile entrypoints:

• black: Reformat code with black
• check-black: Check if code has been reformatted
• isort: Reorganize imports with isort
• check-isort: Check if code has been reorganized

Additionally it adds the base "lint" entrypoint which eventually will run all linters like flake8, mypy, etc.

The pyproject.toml configuration is largely based on https://github.com/freedomofpress/securedrop/pull/6722, which moved configuration out of the Makefile. Linting everything instead of specific folders will make it much easier to copy around to other repositories and reduce variance.

[legoktm]

Also, wondering if we should have a list in the README of tools that this repo configures.

[gonzalo-bulnes]

@cfm Feel free to dismiss my review once stale and move forward!

[gonzalo-bulnes]

Also, wondering if we should have a list in the README of tools that this repo configures.

I think that'd be useful 👍 if only to see at a glance if the repo contains any config about tool X that's you're about to set up in repo Y.

[gonzalo-bulnes]

For the record: the value of a do-nothing script for this first stage (black, isort) is low, and the effort involved might actually be similar to automating some steps entirely. We're keeping those ideas in mind for the future and moving forward without actions on that side for now.

[gonzalo-bulnes]

@legoktm Heads up the commits are not currently signed. :lock_with_ink_pen:

[legoktm]

@cfm done!