Add Kafka interconnection extension with routing, CloudEvent flow, and loop guard

[krital]

Summary

• add new kafka-extension module with factory, protocol, logging, service registration, and module docs
• add configurable Kafka routing rules for push/pull links (keys, partition, headers, consumer overrides)
• add loop protection (loopGuard.* + per-link loop.allow_same_topic) to prevent topic ping-pong
• add CloudEvent wrapping mode (cloud_event.mode, cloud_event.type, cloud_event.source) while preserving payload and typed metadata
• preserve typed MAPS fields via maps.type.* + maps.data.* headers across round-trips
• add detailed Kafka installation/runtime library/contribution documentation and root README quickstart examples

Testing

• mvn -q -pl kafka-extension test

Notes

• no generated artifacts committed
• root config templates updated with Kafka/CloudEvent examples