Prometheus metrics naming doesn't follow the convention

[maxkrivich]

Just want to raise a general concern about namings and units which are used in the PrometheusMonitor class to expose metrics. You are not obligated to follow the naming convention but it is highly recommended by the Prometheus team.

Things to take a look at:

1. namespaces
2. base units
3. metrics naming

Link on the official Prometheus documentation:
https://prometheus.io/docs/practices/naming/

[Kuzyashin]

HI! Check same feature here : faust-streaming/faust#120