[docs] Instance Config YAML refactor
Refactoring instance page YAML to break out from giant YAML block, instead utilizing a bunch of smaller blocks. Added some explanations, etc. as well.
For preview, see: https://dagster-git-sid-mysqldocs-elementl.vercel.app/deployment/dagster-instance (via https://github.com/dagster-io/dagster/pull/3890). Note that this pull request was for the first revision so some of the typos etc. have been fixed.
Test Plan: bk
Reviewers: sashank, yuhan
Reviewed By: sashank
Differential Revision: https://dagster.phacility.com/D7019