static hello (userAgent, authToken, routing = null, patchs = null) {
    const metadata = Object.assign({ user_agent: userAgent }, authToken)
    if (routing) {
      metadata.routing = routing
    }
    if (patchs) {
      metadata.patch_bolt = patchs
    }
    return new RequestMessage(
      HELLO,
      [metadata],
      () => `HELLO {user_agent: '${userAgent}', ...}`
    )
  }
Create a new HELLO message.
@param {string} userAgent the user agent.
@param {Object} authToken the authentication token.
@param {Object} optional server side routing, set to routing context to turn on server side routing (> 4.1)
@return {RequestMessage} new HELLO message.