Implement custom Drupal Entities that use commercetools as storage

Problem/Motivation

Now the module operates with commercetools GraphQL result models to render the products. To customize the output users can use event subscribers to modify and extend the products by custom Drupal logic.

Proposed resolution

To simplify extending and bring more Drupal-specific functionality, would be great to implement a custom Drupal Entity Type which will use commercetools GraphQL as a storage, and implement full-featured Drupal entities from the commercetools models.

It should allow implementing integration with Drupal Fields API, Views, and many other Drupal-specific things out of the box.

Remaining tasks

User interface changes

API changes

Data model changes