Revised the Parametrizing Solid with Config in Docs Basics of Solids

Summary:

1. Created a new config.py for parametrizing-solids-with-config. Wrote a new config.py and its test: test_config.py.
2. The image is modified manually. I'll update all the screenshots after learning how to use generate_screenshots.test.js

Latest Preview by 10/19 PM:

Test Plan: test_config.py

Reviewers: yuhan, max, sashank, schrockn

Reviewed By: schrockn

Differential Revision: https://dagster.phacility.com/D4719