class_docstr: Attaches the given image to the PagerDuty request
  
  Works for both the v1 and v2 event api integrations.
  
  It is recommended to subclass this class with your own implementation of _image_url(),
  _click_url() and _alt_text() so that you can customize your own image.
code: def _image_url(cls):
      return cls.IMAGE_URL
  
file_path: streamalert/publishers/community/pagerduty/pagerduty_layout.py
imports: from publishers.community.generic import StringifyArrays
  from streamalert.shared.publisher import AlertPublisher, Register
label_desc: Use image node_id 2 for calling the AttachImage obj's underlying member method code with example usage: obj._image_url(cls) and returns: cls