Add ClientId and ClientHost to consumer group partition metrics

[theY4Kman]

This PR adds the Client ID and Client Host to the kafka_consumergroup_current_offset and kafka_consumergroup_lag metrics, which describe the group member (if any) assigned to the particular partition.

kafka_consumergroup_current_offset{client_host="/1.2.3.4",client_id="my.consumer.2",consumergroup="log_ingestion",partition="11",topic="logs"} 1.1231975e+07

kafka_consumergroup_lag{client_host="/1.2.3.1",client_id="my.consumer.1",consumergroup="log_ingestion",partition="4",topic="logs"} 0

[kenwoodjw]

awesome

[kenwoodjw]

I build your pr code ,It work perfect