Improve JSON type coercion

[nasdf]

The JSON input type should be able to handle any valid GQL type and not just strings.

This is how mutations with JSON fields currently work:

mutation {
  create_Users(input: {custom: "{\"tree\": \"maple\", \"age\": 250}"}) {
    custom
  }
}

This is how they should work:

mutation {
  create_Users(input: {custom: {tree: "maple", age: 250}}) {
    custom
  }
}