[CT-105] use black code formatter

[kwigley]

Let's introduce the automated code formatting to dbt as long as it does not sacrifice readability. As the codebase matures, it will be nice to not have to think about formatting, generate clean diffs, and maintain a single code style.

black code formatter docs

First, run on a subset of files and get feedback from contributors about stylistic decisions. We may need to tweak line length and other knobs to our liking.
Then:

• Add black as a dev dependency
• Update tox.ini and where tox code checks are run in CI and Makefile. May need 2 different tox envs, one to check formatting and one to actually run the formatter
• Get the changes above reviewed
• Finally, create a commit that runs the formatter on the whole repo and set the author of the commit to a machine user so we can easily determine blame history.

[github-actions]

This issue has been marked as Stale because it has been open for 180 days with no activity. If you would like the issue to remain open, please remove the stale label or comment on the issue, or it will be closed in 7 days.

[leahwicz]

Closing the other as a dupe and just using this one