[lakehouse] RFC: bake policies into storage defs
Summary: I got frustrated with all the code that was required to define a basic lakehouse. This simplifies the storage interface - a storage now just saves and loads stuff. For the multi-type case where we have different ways of saving / loading Spark DFs vs. Pandas DFs, there's a special storage implementation that dispatches to sub-storages.
Test Plan: bk
Reviewers: alangenfeld, schrockn
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D3883