Add ability to detect the model class implicitly.

[aditya-kapoor]

Part of #7

Now while defining new types, if you the automatic detection will first try to detect the class upon the code initialization.

BEFORE

module Types
  class SessionType < ApplicationType
    model_class Session
  
    attribute :token

    relationship :user
  end
end

AFTER

module Types
  class SessionType < ApplicationType
    attribute :token

    relationship :user
  end
end

[RabidFire]

Rename _attribute to common_attribute - As per our style guide, we prefix with underscore for unused vars: https://github.com/rubocop-hq/ruby-style-guide#underscore-unused-vars

[RabidFire]

1. I would simplify to:

return if @attributes_initialized.include?(name)
@attributes_initialized.add(name)

2. Since model_class is no longer required, we need to call initialize_common_attributes in both attribute and model_class.

initialize_common_attributes

3. Remove the all_initial_attributes_added? method as the check would be present within the attribute method itself.

[aditya-kapoor]

1. the above check for the @attributes_initialized is to prevent the recursion and would create the duplicate types. This is just the mechanism to control the recursion when we want to run the intialize_common_attributes.

2. We still need the model_class method in those scenarios when the Automatic type detection failed. See: https://github.com/Amandeepsinghghai/sample-graphql-app/blob/tmp-work/app/graphql/types/optional_user_type.rb#L3

3. I am all ears, on this, I also felt that this can improved.

[RabidFire]

Remove @attributes_initialized.add(_attribute) from within initialize_common_attributes as that it is being handled by attribute method.

[aditya-kapoor]

I need to add the attribute to the @attributes_initialized Set, so that it won't be called again from the attribute method.