chore: import upstream snapshot with attribution

doc/source/ray-core/patterns/actor-sync.rst

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+Pattern: Using an actor to synchronize other tasks and actors
+=============================================================
+
+When you have multiple tasks that need to wait on some condition or otherwise
+need to synchronize across tasks & actors on a cluster, you can use a central
+actor to coordinate among them.
+
+Example use case
+----------------
+
+You can use an actor to implement a distributed ``asyncio.Event`` that multiple tasks can wait on.
+
+Code example
+------------
+
+.. literalinclude:: ../doc_code/actor-sync.py