Explore the possibility of using multiple topics and or restructure the kafka opmon stream

[mroda88]

At the moment the opmon stream is the most demanding in terms of message frequency. It's still not a major issue in terms of CPU consumption, but we might want to think about how to structure in a more elegant way the kafka opmon stream.
This will require the understanding of the system load once the kafka stream will be used by all users and partitions.