Allow to have underscore model field names

[povilasjurcys]

All model fields are camelized and there is no way how to change this. It would be nice to have option to do so, something like this:

class User
  include GraphqlRails::Model

  graphql do |c|
    c.attribute :underscored_name, type: :string!, name_format: :original
  end
end