Export BatchBucketOneHot Caffe2 Operator to PyTorch
Summary: As titled.
Test Plan:
```
buck test caffe2/caffe2/python/operator_test:torch_integration_test -- test_batch_bucket_one_hot_op
```
Reviewed By: yf225
Differential Revision: D23005981
fbshipit-source-id: 1daa8d3e7d6ad75e97e94964db95ccfb58541672
