Add rd_kafka_DescribeLogDirs admin API

[Piotr WOLSKI (piochelepiotr)]

Summary

Implements the DescribeLogDirs admin API (Kafka API key 35, KIP-113) to allow querying partition sizes in bytes on disk for capacity planning and monitoring.

• Adds full C admin API following the ElectLeaders pattern (self-contained protocol request/response)
• Supports protocol versions 0-4 with flexible version negotiation (v2+)
• topics parameter accepts a topic-partition list to filter, or NULL for all topics
• Request targets a specific broker via AdminOptions_set_broker(), defaults to controller
• No fanout: single broker per call (same as Java AdminClient)

Resolves #5192

Changes

• src/rdkafka_op.h/c — New RD_KAFKA_OP_DESCRIBELOGDIRS op type
• src/rdkafka.h — Public API: event define, typedefs, opaque types, function declarations, accessors
• src/rdkafka_admin.h — Internal structs for LogDirDescription, LogDirTopicDescription, LogDirPartitionDescription
• src/rdkafka_request.h/c — Protocol request builder with v0-v4 negotiation
• src/rdkafka_admin.c — Entry point, response parser, result types, all public accessors
• src/rdkafka_event.h/c — Event type registration and getter
• tests/0080-admin_ut.c — Unit tests (4 variants: main/temp queue × with/without options)

Test plan

• cmake build succeeds with no new warnings
• ./tests/test-runner 0080 passes all existing and new tests
• Manual test against local Kafka broker at localhost:9092 (if available)

🤖 Generated with Claude Code

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