Kafka gateway: Kafka gateway Phase 2 — E2E tests with consumer groups

[ryerraguntla]

Part of #3560.

Summary

End-to-end validation of Phase 2 consumer group support.

Depends on

• Kafka gateway: Kafka OffsetCommit and OffsetFetch with persisted consumer offsets #3542 — OffsetCommit / OffsetFetch
• Kafka gateway: Kafka LeaveGroup and consumer group rebalance semantics #3543 — LeaveGroup / rebalance

Scope

• kafka-console-consumer.sh --bootstrap-server ... --group test-group --topic ...
• Multi-consumer same group integration test
• Offset commit + bridge restart + resume test
• Update README: Phase 2 capabilities and limits
• Update discussion feature - Order of Implementation discussion of kafka to iggy bridge #3253 with issue links

Acceptance criteria

• All Phase 2 success metrics from discussion feature - Order of Implementation discussion of kafka to iggy bridge #3253 met
• CI covers consumer group happy path

References

• Rollout plan: feature - Order of Implementation discussion of kafka to iggy bridge #3253 (comment)