Expose all Kafka Connect metrics through JMX

[brianhafferkamp]

Right now, it looks like we're only exposing 3 sets of Kafka Connect metrics in the jmx-configmap. According to the Confluent Docs, these seem to be the:

• Common Task Metrics
• Worker Metrics
• Client Metrics.

It would be great if we could add in the additional metrics as defined by the docs:

• Connector Metrics
• Worker Rebalance Metrics
• Source Task Metrics
• Sink Task Metrics

[patelamol]

These metrics are really crucial on getting an insights into how the connectors are behaving in different situation. Is there are PR open already for this?