NN Descent supports multiple metrics, and the batched NN Descent is not passing the metric argument properly. Need to pass the metric to `BuildConfig` [here](https://github.com/rapidsai/cuvs/blob/89b03493b487910d2125fde6680590adde8e2a95/cpp/src/neighbors/detail/nn_descent_batch.cuh#L653), like we are doing [here](https://github.com/rapidsai/cuvs/blob/89b03493b487910d2125fde6680590adde8e2a95/cpp/src/neighbors/detail/nn_descent.cuh#L1495).
