Extends user-events configuration

* The Prometheus recorder can't be disabled in the current `user-events` implementation.
Someone might want to use the KamonRecorder with some reporters other than Prometheus. It would be better to make the `reporter` and `recorder` configurable.
https://github.com/apache/openwhisk/blob/f04275a825346da52d8616cf241f7a6ae78dccbc/core/monitoring/user-events/src/main/scala/org/apache/openwhisk/core/monitoring/metrics/OpenWhiskEvents.scala#L49
* Make kafka `client.id` configurable in order to be able to run multiple instances of the this service.
https://github.com/apache/openwhisk/blob/f04275a825346da52d8616cf241f7a6ae78dccbc/core/monitoring/user-events/src/main/scala/org/apache/openwhisk/core/monitoring/metrics/EventConsumer.scala#L138

Start with core/monitoring/user-events/src/main/scala/org/apache/openwhisk/core/monitoring/metrics/OpenWhiskEvents.scala around line 49 and EventConsumer.scala around line 138. Trace the existing reporter, recorder, and Kafka client configuration, then check the related user-events configuration and tests. Done means the Prometheus recorder can be disabled or replaced, and Kafka client.id can be set for multiple service instances.

Written by the indexing model from the issue text.