Add black and isort with pre-commit?

[yarikoptic]

which would entail black'ning the entire code base while at it, should also include sorting of imports (isort) for a good measure.
We have been using such tandem in dandi-cli and I quite like it. @mslw also expressed his liking in datalad/datalad-extension-template#45 (comment) for redcap extension.

Will do after we merge #190 if no objections voiced. Would be a "test bed" for possible future suggestion for datalad-extensions-template ;)