static fromRequest(request, user, result) {
    return new UserNotification({
      action: request.input.action,
      collection: request.input.resource.collection,
      controller: request.input.controller,
      index: request.input.resource.index,
      node: global.kuzzle.id,
      protocol: request.context.connection.protocol,
      result,
      status: 200,
      timestamp: request.timestamp,
      user,
      volatile: request.input.volatile,
    });
  }
Instantiates a UserNotification object from a KuzzleRequest
@param {Request} request - the request object from which the notification is issued
@param {string} user - The scope of the notification (in or out)
@param {object} content - Notification content
returns {UserNotification}