Please rewrite it as a function. We do not want someone overwriting `defaultConfig` from the output setup step.    ```golang  func defaultConfig() Config {      return Config{          TLS:         nil,  \tTimeout:     30 * time.Second,  \tMaxRetries:  3,  \tBulkMaxSize: 50,  \tBackoff:     FromGRPCBackOff(backoff.DefaultConfig),      }  }  ```