code: public function relatedResource($resourceType, $id, $relationshipKey, array $queryParams = [])
      {
          return $this->resource(RouteName::related($resourceType, $relationshipKey), $id, $queryParams);
      }
docs: Get a link to a resource object's related resource.
  
  @param $resourceType
  @param $id
  @param $relationshipKey
  @param array $queryParams
  @return string