List consumer group offsets

[PratRanj07]

Created ListConsumerGroupOffsets API with the name of fetchOffsets and wrote examples and test cases for it.

[cla-assistant[bot]]

All committers have signed the CLA.

[EricMCornelius]

Any ETA on this? You guys are promoting this client as a KafkaJS replacement while lacking some pretty basic functionality on the admin side here...

[EricMCornelius]

https://github.com/confluentinc/confluent-kafka-javascript/blob/master/MIGRATION.md#admin-client

At the very least, maybe keep major omissions up to date in any migration guides?

[confluent-cla-assistant[bot]]

:tada: All Contributor License Agreements have been signed. Ready to merge.
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