Allow multi-node commands in async pipeline

[Yard1]

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Description of change

While RedisCluster.execute_command supports multi-node commands (and returns a dictionary of {node.name: result}), ClusterPipeline did not allow for it. This PR adds support for multi-node commands in ClusterPipeline. The results of those commands will be put into the returned list in format consistent with RedisCluster.execute_command.