PM - Document PM reporting formats on Kafka bus

In order to define how systems northbound of VOLTHA (Controller, OSS, EMS) consume reported PM interval measurements from VOLTHA -

• Document the interface for consumers, including -
•  the Kafka topic for subscription by these consumers
•  the reported PM Interval measurements
• input to the sizing of the Kafka bus for a defined scale capacity of OLTs and ONUs managed in VOLTHA from the maximum amount of reported PM interval measurements

This should be an activity in the documentation phase of the release.