text: Title: Add support for combined unique constraints
  Body: ## Problem
  
  <!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] -->
  
  Prisma supports declaring multiple fields as a combined unique constraint, e.g.
  
  ```prisma
  model User {
    firstName String
    lastName  String
  
    @@id([firstName, lastName])
  }
  ```
  