refactor `black` check to be configured in pyproject.toml instead of ci.yml

`black` formatting is currently opt-in by specifying `ValidateFormatting: true` in a library's ci.yml: https://github.com/Azure/azure-sdk-for-python/blob/main/doc/eng_sys_checks.md#opt-in-to-formatting-validation

We should refactor this check to instead be turned on/off by the pyproject.toml where other checks like pylint, mypy, pyright, and sphinx are controlled.