Extract common Kafka stream methods from EventClient

~~It seems from the kafka-python api [docs](https://kafka-python.readthedocs.io/en/master/apidoc/KafkaConsumer.html) that a KafkaConsumer can receive an optional list of topics to subscribe to. It would be nice that [EventClient](https://github.com/MetaCell/cloud-harness/blob/develop/libraries/cloudharness-common/cloudharness/events/client.py#L48) would allow the same instead of forcing one and one only topic.~~

Edited after discussing with @zsinnema:

CH could have the common Kafka stream methods extracted to a new class, so that it can support different use cases

Start in libraries/cloudharness-common/cloudharness/events/client.py at the EventClient implementation, then compare its behavior with the kafka-python KafkaConsumer API. Identify the common Kafka stream methods that belong in a new class; the work is done when EventClient and other intended use cases can use that shared abstraction, including the discussed topic-subscription behavior.

Written by the indexing model from the issue text.