Changes to GET /api/v1/:context_id/principals

the response's body type changed from array to object for status 200

added the new optional query request parameter count

added the new optional query request parameter cursor

added the new optional query request parameter limit

added the non-success response with the status 400

added the non-success response with the status 503

added the required property page to the response with the 200 status

added the required property principals to the response with the 200 status