Scale up processing of change events

Increase the number of change event queues and queue processors to parallelize the processing and publishing of change events. Commit log files are only moved out from cdc_raw directory when all change events related with this file have been published to Kafka. Because of this, we want to make sure that change events are processed and published fast so that commit log files won't pile in cdc_raw directory, which will potentially cause write suspension in Cassandra DB.