Major Description
In order to properly monitor individual tasks using the producer and consumer metrics, we need to have the framework disambiguate them. Currently when we create producers (https://github.com/apache/kafka/blob/trunk/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/Worker.java#L362) and create consumers (https://github.com/apache/kafka/blob/trunk/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/WorkerSinkTask.java#L371-L394) the client ID is not being set. You can override it for the entire worker via worker-level producer/consumer overrides, but you can't get per-task metrics.
There are a couple of things we might want to consider doing here:
1. Provide default client IDs based on the worker group ID + task ID (providing uniqueness for multiple connect clusters up to the scope of the Kafka cluster they are operating on). This seems ideal since it's a good default; however it is a public-facing change and may need a KIP. Normally I would be less worried about this, but some folks may be relying on picking up metrics without this being set, in which case such a change would break their monitoring.
2. Allow overriding client.id on a per-connector basis. I'm not sure if this will really be useful or not – it lets you differentiate between metrics for different connectors' tasks, but within a connector, all metrics would go to a single client.id. On the other hand, this makes the tasks act as a single group from the perspective of broker handling of client IDs.
