Add mock for the consumer group

[XSAM]

Versions

Sarama	Kafka	Go
1.26.4

Problem Description

I am working with adding tracing instrumentation for the Sarama consumer group. Still, there is a problem that the consumer group does not have a mock implement, thereby is hard to write a unit test.

[unflag]

It would be very useful for unit testing. Is there any plans on this feature?

[github-actions]

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