[CT-238] Add black formatter and precommit hooks

[leahwicz]

Following the changes in dbt-core, let's add the black formatter and precommit hooks to the repo.

Follow the example done in dbt-core:

• Example precommit hook PR: Pre commit Hooks (black, flake8, mypy, etc) [CT-105] dbt-core#4639
• Example formatter PR: Reformat core [CT-104 CT-105] dbt-core#4697

CC: @iknox-fa for questions