Changes to Get A/B test stats

added the new event_rate enum value to the significance/metric response property for the response status 200

added the new goal_conversion_rate enum value to the significance/metric response property for the response status 200

added the new goal_value enum value to the significance/metric response property for the response status 200

added the optional property variants/items/outcome to the response with the 200 status

added the optional property issues to the response with the 400 status

added the optional property issues to the response with the 401 status

added the optional property issues to the response with the 404 status

added the optional property issues to the response with the 503 status

added the optional property significance to the response with the 200 status

added the optional property retryable to the response with the 400 status

added the optional property retryable to the response with the 401 status

added the optional property retryable to the response with the 404 status

added the optional property retryable to the response with the 503 status

added the non-success response with the status 503

added the optional property code to the response with the 400 status

added the optional property code to the response with the 401 status

added the optional property code to the response with the 404 status

the response property success became optional for the status 400

the response property success became optional for the status 401

the response property success became optional for the status 404

added the new optional query request parameter includeMachineEngagement

endpoint added