code: def timestamp_insert(sender, frames):
          
          for frame in frames:
              timestamp = datetime.now(timezone.utc)
              frame.created = timestamp
              frame.modified = timestamp
docs: Timestamp the created and modified fields for all documents. This method
          should be bound to a frame class like so:
  
          ```
          MyFrameClass.listen('insert', MyFrameClass.timestamp_insert)
          ```