code: def exec_event(event, webhooks, payload):
      
      calls = (
          call_webhook.s(event, webhook, payload)
          for webhook in webhooks
      )
      callback = merge_webhooks_runset.s()
  
      call_promise = chord(calls)
      promise = call_promise(callback)
      return promise
docs: Execute event.
  
      Merge webhooks run set to do some stats after all
      of the webhooks been responded successfully.
  
      +---------+
      |webhook-1+--------------------+
      +---------+                    |
                                     |
      +---------+                    |
      |webhook-2+-------------+      |
      +---------+             +------+-----+
                              |merge runset+------>
      +---------+             +------+-----+
      |webhook-3+-------------+      |
      +---------+                    |
                                     |
      +---------+                    |
      |...      +--------------------+
      +---------+
  
  
      Error webhook will be propagated. Note that other webhook
      calls will still execute.