chore: import upstream snapshot with attribution

python/ray/train/horovod/__init__.py

@@ -0,0 +1,22 @@
+# isort: off
+try:
+    import horovod  # noqa: F401
+except ModuleNotFoundError:
+    raise ModuleNotFoundError(
+        "Horovod isn't installed. To install Horovod with PyTorch support, run 'pip "
+        "install 'horovod[pytorch]''. To install Horovod with TensorFlow support, "
+        "run 'pip install 'horovod[tensorflow]''."
+    )
+# isort: on
+
+from ray.train.horovod.config import HorovodConfig
+from ray.train.horovod.horovod_trainer import HorovodTrainer
+from ray.train.v2._internal.constants import is_v2_enabled
+
+if is_v2_enabled():
+    from ray.train.v2.horovod.horovod_trainer import HorovodTrainer  # noqa: F811
+
+__all__ = ["HorovodConfig", "HorovodTrainer"]
+
+
+# DO NOT ADD ANYTHING AFTER THIS LINE.