telemetry ({ api }, { onError, onCompleted } = {}) {
    const observer = new CompletedObserver()
    if (onCompleted) {
      onCompleted()
    }
    return observer
  }
Send a TELEMETRY through the underlying connection.

@param {object} param0 Message params
@param {number} param0.api The API called
@param {object} param1 Configuration and callbacks
@param {function()} param1.onCompleted Called when completed
@param {function()} param1.onError Called when error
@return {StreamObserver} the stream observer that monitors the corresponding server response.