Update default python version for python models

[mikealfare]

resolves #1203

Problem

We are defaulting to an EOL version of Python when the user does not specify a python version in their python models. This was missed because it is buried in the code.

Solution

• Create a new settings module
  • Open to renaming, but we need to avoid things like config that get used everywhere
• Update from Python 3.8 to Python 3.9 by referencing a new setting in the settings module

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX