Expose Category Key in request reponse for Category ID so user can render dynamic category pages

User Story: As User I would like to render dynamic Category pages by calling it by the Category Key instead of only CategoryID so that I can get my pages from the commerceTools 

Background: our Client's Avon  users is facing a difficulties with rendering  dynamic category pages. Currently our framework offers to call it directly via below params:
private final Id id;
private final String name;
private final String description;
private final Integer position;
private final Integer level;
private final String parentId;
private final String path;
 

Requirement: We need to somehow expose Category Key without interrupting our framework structure (so the solution won't be one customer oriented). Would be great to try reach as lowest amount of request as possible for the customer. 

Acceptance Criteria:

Given: User has integrated CustomerTools with Magnolia Commerce Connector Pack 
When: He request for all Categories or Category by single ID 
Then: He receives Category Key in response

outcome: He can filter the categories by the key provided in the response
and 
Then: He can render the (filtered) categories