Add support to run MLServer in Windows

[adriangonz]

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Currently, the MLServer CLI won't be able to run in Windows. The main blocker we've found for this is that the add_signal_handler method is not supported in Windows AsyncIO loops (because Windows doesn't have signals). However, there could be other blockers behind this.

https://github.com/SeldonIO/MLServer/blob/565b3b2a075b82b25aa7727de492a9056e8ee59c/mlserver/server.py#L74