KIP-545 — support automated consumer offset sync across clusters in MM 2.0

Accepted Kafka 2.7 MirrorMaker

KIP-545 adds a `sync.group.offsets.enabled` MirrorMaker 2 configuration that, when combined with `emit.checkpoints.enabled`, periodically writes translated consumer offsets into the target cluster's `__consumer_offsets` topic automatically. Previously, offset translation from the source cluster was available via `MirrorClient.remoteConsumerOffsets()` but had to be driven by external tooling; without automatic sync, consumers failing over to the target cluster cannot resume from their last committed position without manual intervention.

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