Add support for custom directives.

[Atlinx]

Although we already have the @schema(metadata: []) decorator, it would nice if we could write our own decorators to make our gql schema less verbose. These decorators could be placed under the existing metadata field, or in it's own unique field.

Ex.
GraphQL

type User @entity @mongodb {
  id: ID! @id(from: "db") @alias(value: "_id")
  createdAt: Date! @createdAt # This is a custom decorator
  name: Date! @deprecated(reason: "Use firstName + lastName") # This is a custom decorator
  firstName: String
  lastName: String
  @@unique(fields: ["firstName", "lastName"]) # This is a custom decorator
}

Schema

export function userSocialSchema(): T.Schema<types.Scalars> {
  return {
    id: {
      type: 'scalar',
      scalar: 'ID',
      isId: true,
      generationStrategy: 'db',
      required: true,
      alias: '_id',
    },
    createdAt: {
      type: 'scalar',
      scalar: 'String',
      required: true,
      directives: [
        {
          name: "createdAt",
        }
      ]
    },
    name: {
      type: 'scalar',
      scalar: 'String',
      required: true,
      directives: [
        {
          name: "deprecated",
          args: {
            reason: "Use firstName + lastName"
          }
        }
      ]
    },
    firstName: {
      type: 'scalar',
      scalar: 'String',
    },
    lastName: {
      type: 'scalar',
      scalar: 'String',
    },
    __directives: {
      {
        name: "unique",
        args: {
          fields: [ "firstName", "lastName" ]
        }
      }
    }
  }
}

[edobrb]

I like it, it's seems reasonable. What do you think @minox86 ?

[minox86]

I'd like it. Just a point of attention: is it better to define a "typetta abstraction" for directives or to simply add a reference to the GraphQL AST in the Schema?