text: Title: Provide a JSON Schema generator
  Body: ## Problem
  
  This would be useful as a real world example of a custom Prisma generator.
  
  It could also help find any features we could add that would make building custom Prisma generators easier.
  
  ## Additional context
  
  This has already been implemented in TypeScript: https://github.com/valentinpalkovic/prisma-json-schema-generator