class_docstr: ArgoEvent is a small event, a message, that can be published to Argo Workflows. The
  event will eventually start all flows which have been previously deployed with `@trigger`
  to wait for this particular named event.
  
  Parameters
  ----------
  name : str,
      Name of the event
  url : str, optional
      Override the event endpoint from `ARGO_EVENTS_WEBHOOK_URL`.
  payload : Dict, optional
      A set of key-value pairs delivered in this event. Used to set parameters of triggered flows.
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docstr: Add a key-value pair in the payload. This is typically used to set parameters
  of triggered flows. Often, `key` is the parameter name you want to set to
  `value`. Overrides any existing value of `key`.
  
  Parameters
  ----------
  key : str
      Key
  value : str
      Value
docstr_tok: ["Add","a","key-value","pair","in","the","payload",".","This","is","typically","used","to","set","parameters","of","triggered","flows",".","Often",",","`","key","`","is","the","parameter","name","you","want","to","set","to","`","value","`",".","Overrides","any","existing","value","of","`","key","`",".","Parameters","--","--","--","--","--","key",":","str","Key","value",":","str","Value"]
code: def add_to_payload(self, key, value):
      """
      Add a key-value pair in the payload. This is typically used to set parameters
      of triggered flows. Often, `key` is the parameter name you want to set to
      `value`. Overrides any existing value of `key`.
  
      Parameters
      ----------
      key : str
          Key
      value : str
          Value
      """
  
      self._payload[key] = str(value)
      return self
  
file_path: metaflow/metaflow/plugins/argo/argo_events.py
imports: import json
  import os
  import sys
  import time
  import urllib
  import uuid
  from datetime import datetime
  from metaflow.exception import MetaflowException
  from metaflow.metaflow_config import ARGO_EVENTS_WEBHOOK_AUTH, ARGO_EVENTS_WEBHOOK_URL, SERVICE_HEADERS
label_desc: Use image node_id 2 for calling the ArgoEvent obj's underlying member method code with example usage: obj.add_to_payload(key, value) and returns: self