[metricbeat][Kafka] Improve error logging

[stefans-elastic]

There is at least one place i the module where error itself isn't logged which makes it difficult to troubleshoot -

beats/metricbeat/module/kafka/consumergroup/query.go

Line 120 in ff9d3fa

logger.Errorf("failed to fetch offset for (topic, partition): ('%v', %v)", topic, partition)

Update the log statement to include error itself. Check for any other places in the code where log statement might be lacking error.

[botelastic]

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