Improve pub-sub performance

The probable cause of performance issues in pub-sub lies in running out of memory by putting too much on the write queue of KafkaProducer. To fix the issue try the following:

• Upon receiving an event - respond before sending event to kafka
• Remove redundant querying of the db for getting messaging modules by caching
• Replace single shared KafkaProducer with other option KafkaProducer
• Add logging to pub-sub