[3/n init_resources] Resource initialization refactor
This diff refactors the existing code path for resource initialization.
- Makes various top level args Noneable on the resource initialization manager.
- Adds a new config wrapper around resource config.
Test Plan: Changed tests to reflect new resource config wrapper.
Reviewers: sandyryza, alangenfeld, max
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D6513