create input should be "optional"

[yaquawa]

Take the example from the README:

type Post @model {
  id: ID!
  title: String! @default(value: "hello world")
  viewCount: Int @default(value: "9001")
  tag: Tag @default(value: "RANDOM")
}
enum Tag {
  NEWS
  RANDOM
}

the title field is a non-nullable field, but it should not be a required argument in the createXXX input type, that will be nonsense because we already have a default value now.