Extended enum to model binding tips

Using the following recipe you can bind enum values to specific const or variable. Both typed and untyped binding are supported.

For typed:
Set model to const/var type. Set enum values to specific const/var.
For untyped:
Set model to predefined gqlgen type (e.g. for int use github.com/99designs/gqlgen/graphql.Int). Set enum values to specific const/var.

More examples can be found in _examples/enum.

Binding target go model enums:

package model

type EnumTyped int

const (
	EnumTypedOne EnumTyped = iota + 1
	EnumTypedTwo
)

const (
	EnumUntypedOne = iota + 1
	EnumUntypedTwo
)

Binding using @goModel and @goEnum directives:

directive @goModel(
    model: String
    models: [String!]
) on OBJECT | INPUT_OBJECT | SCALAR | ENUM | INTERFACE | UNION

directive @goEnum(
    value: String
) on ENUM_VALUE

type Query {
    example(arg: EnumUntyped): EnumTyped
}

enum EnumTyped @goModel(model: "./model.EnumTyped") {
    ONE @goEnum(value: "./model.EnumTypedOne")
    TWO @goEnum(value: "./model.EnumTypedTwo")
}

enum EnumUntyped @goModel(model: "github.com/99designs/gqlgen/graphql.Int") {
    ONE @goEnum(value: "./model.EnumUntypedOne")
    TWO @goEnum(value: "./model.EnumUntypedTwo")
}

The same result can be achieved using the config:

models:
  EnumTyped:
    model: ./model.EnumTyped
    enum_values:
      ONE:
        value: ./model.EnumTypedOne
      TWO:
        value: ./model.EnumTypedTwo
  EnumUntyped:
    model: github.com/99designs/gqlgen/graphql.Int
    enum_values:
      ONE:
        value: ./model.EnumUntypedOne
      TWO:
        value: ./model.EnumUntypedTwo