Disabling field alias

[danielcondemarin]

Hey 👋 Thanks for your work on this library.

I wanted to confirm my approach to disable aliases is correct. I was looking to implement something like https://github.com/ivandotv/graphql-no-alias in gqlgen & came up with this directive,

        func NoAlias(ctx context.Context, _ interface{}, next graphql.Resolver) (res interface{}, err error) {
		opCtx := graphql.GetOperationContext(ctx)
		fieldCtx := graphql.GetFieldContext(ctx)
		fieldName := fieldCtx.Field.Name

		var count int
		for _, s := range opCtx.Operation.SelectionSet {
			if f, ok := s.(*ast.Field); ok {
				if fieldName == f.Name {
					count++
				}
			}
		}

		if count > 1 {
			return nil, fmt.Errorf("\"%s\" was requested multiple times", fieldName)
		}

		return next(ctx)
	}

Would you say this is a good approach? Relying on opCtx.Operation.SelectionSet seems to work well.