Our Kafka Grafana dashboards shows currently 4 different rates:

• Bytes in
• Bytes out
• Produce requests
• Incoming messages

These are currently configures without any actual unit, just with the unit being described in postfix. Especially with the bytes in and out rates this looks really stupid when you use it with some busy cluster, because it shows 500MB/s in B/s which is very hard to read.

This PR changes these metrics units to rates. They should be better formatted - for example for the bytes in our out Grafana would automatically use the fitting unit.