Replace use of deprecated DirectProcessor

[edwin-greene]

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👾 Description of the issue

SharedTopicListener uses reactor.core.publisher.DirectProcessor, which is deprecated.

Solution

Update SharedTopicListener to use Project Reactor Sinks.

Ensure the Sink implementation is as performant as the DirectProcesser. That can be done by creating a JMH test for SharedTopicListener. It would be great to have it but it is not a must to solve the issue.

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[saai-syvendra]

I'll work on this issue

[steven-sheehy]

Thanks @saai-syvendra. I've assigned you the issue. Let me know if you need any guidance.