class_docstr: StreamAlertAppPayload class
code: def service(cls):
      return "streamalert_app"
  
imports: from streamalert.classifier.payload.payload_base import PayloadRecord, RegisterInput, StreamPayload
  from streamalert.shared import CLASSIFIER_FUNCTION_NAME
  from streamalert.shared.metrics import MetricLogger
label_desc: Use image node_id 1 for calling the AppPayload obj's underlying member method code with example usage: obj.service(cls) and returns: str