Support for multiple order fields through an edge

[henrywoody]

It would be great to have support for multiple order fields through a single edge.

• I have searched the issues of this repository and believe that this is not a duplicate.

Summary 💡

Say you have a schema like this:

// User model

func (User) Fields() []ent.Field {
	return []ent.Field{
		field.String("first_name").
			Annotations(entgql.OrderField("FIRST_NAME")),
		field.String("last_name").
			Annotations(entgql.OrderField("LAST_NAME")),
	}
}

// Book model

func (Book) Edges() []ent.Edge {
	return []ent.Edge{
		edge.From("author", User.Type).
			Ref("books"),
	}
}

And you want to be able to order by the author's first name or last name.

Could look like this:

func (Book) Edges() []ent.Edge {
	return []ent.Edge{
		edge.From("author", User.Type).
			Ref("books").
			Annotations(
				entgql.OrderFields("AUTHOR_FIRST_NAME", "AUTHOR_LAST_NAME"),
			),
	}
}

Given my (limited) understand of how the templating works I think this API would be the easiest to add, but it could also just be that entgql.OrderField is updated to accept multiple arguments or that you could pass multiple entgql.OrderFields (but that last one seems the most difficult to implement).

Motivation 🔦

One should not be limited to ordering by only one field when ordering through an edge.