[metrics] Introduce metrics to measure CPU cost of Realtime consumption

I am interested in introducing metrics that will convey an idea of realtime consumption cost and throughput:

Some of the metrics I have originally thought of are the following:

- Time to consume an event batch and events per batch consumed and avg event size or batch size.
- Time to consume an individual event and avg size of events.
- Event Consumption throughput (bytes/sec)

My ultimate goal is to be able to estimate the CPU resources to consume a given topic.