[Feature Request] Support for black in Jupyter Notebooks

Hello 👋,

First of all thanks for your hard work for bringing black to VSCode. My autoformatting has become so much more seamless now that I don't need to worry about having it installed in all of my envs/projects.

I was wondering whether you have looked into (apologies if this has been asked before - I did a quick scan but didn't find anything) enabling the use of black in jupyter notebooks. The isort plugin for VSCode has done this and black do mention in their docs that it can be enabled by pip installing `black[jupyter]` (https://black.readthedocs.io/en/stable/getting_started.html). Perhaps this could be a user enabled feature if it is not desired to have this by default? :)

No repository files, tests, or entry points are named. Start by reviewing the existing VS Code isort notebook support and Black's jupyter documentation, then identify how this extension handles formatting requests. Done means Jupyter notebook formatting is supported, with any default or user-enabled behavior matching the agreed feature scope.

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