feat(rotor): make Kafka client logging and librdkafka debug configurable

[tevaum]

What

• Add KAFKA_DEBUG (librdkafka debug facilities, e.g. cgrp,fetch,broker) and KAFKA_CLIENT_LOG_LEVEL
• Wire the logCreator that was left commented out in kafka-config.ts, so client/librdkafka messages reach rotor's logger with their facility tag
• Extract buildKafkaConfig/kafkaClientLogLevel and cover them with unit tests

Why

Rotor pins the Kafka client to logLevel: ERROR with no logCreator, and exposes no way to pass
librdkafka options, so client-side diagnostics are unreachable in a deployed rotor. When a consumer
stops delivering records but stays a live group member (see
confluentinc/confluent-kafka-javascript#476 and #497), rotor logs nothing at all and there is no
supported way to collect the cgrp/fetch output a maintainer needs to diagnose it.

Defaults are unchanged: without the new variables the client still logs at ERROR and no debug
key is set. Note all three levels must align to see librdkafka output —
KAFKA_DEBUG=cgrp,fetch, KAFKA_CLIENT_LOG_LEVEL=debug, and JUAVA_LOG_LEVEL=debug.

translateLevel already existed but was unreferenced; this makes it live.