Multiple schema support

[mcember]

Currently, a deltacat table can store multiple schemas. It's not clear if this will work out of the box like we expect, or if we need to modify this to act more like rivulet dataset.py schemas

Acceptance criteria:

• Rivulet dataset.py uses the deltacat Table (version) model and stores all schemas in that model
• Parity with existing dataset.py features including adding schemas to a table and fetching the "all" schema