Investigate cassandra pub/subs in order to reduce polling intervals but retain performance

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If this works, it should allow us to reduce the pressure on Cassandra (from multiple views streams parallel executions) while keeping the eventsByTag delay low.

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While pubsub can be used to lower latency as advertised in the akka-persistence-cassandra documentation, the tests show that enabling it and increasing significantly the polling interval is not a valid solution to reduce pressure on the primary store as it prevents indexing to work correctly.