Add docs “Message handler patterns” like in Python: - Add sample [like this](https://github.com/temporalio/samples-python/tree/message-passing/message_passing/safe_message_handlers) - Add documentation [like this](https://docs.temporal.io/develop/python/message-passing#message-handler-patterns) - cover `HandlerUnfinishedPolicy`
Add docs “Message handler patterns” like in Python:
HandlerUnfinishedPolicy