Support Prisma "multiSchema" (multiple database schemas)

[dmythro]

Here's a guide, it looks like a pretty simple thing to add: How to use Prisma with multiple database schemas.

Feature is in a preview but we need it so much now :)

To achieve this, we need to support Prisma previewFeatures: string[], specify db schemas: string[] and support @@schema("public") for a List.db.schema?: sting.