Describe the spike

In order to switch to using pyproject.toml we need to spike a few impact/feasibility things:

• Will this break things in dbt-cloud? I'm specifically concerned about our docker images since I know they're a bit fragile install wise.
• Are all of the features we use in setup.py supported in pyproject.toml? Our setuptools setup isn't terribly complex, but there's some uncertainty here (esp in adapter repos re the version checking regex stuff :grimace:)