BigQuery storage settings don't propagate the user-agent header

[kmjung]

This doesn't work:

      BigQueryStorageSettings settings =
          BigQueryStorageSettings.newBuilder()
              .setHeaderProvider(USER_AGENT_HEADER_PROVIDER)
              .build();

This does:

      BigQueryStorageSettings settings =
          BigQueryStorageSettings.newBuilder()
              .setTransportChannelProvider(
                  BigQueryStorageSettings.defaultGrpcTransportProviderBuilder()
                      .setHeaderProvider(USER_AGENT_HEADER_PROVIDER)
                      .build())
              .build();

This seems wrong.