Add diskless.managed.rf.enable config (default: false) to control whether
diskless topics use managed replicas with RF=rack_count or legacy RF=1.

This config only affects topic creation. When enabled, new diskless topics
will be created with one replica per rack using standard KRaft placement.

Part of Phase 1: Diskless Managed Replicas
(See #478 docs/inkless/ts-unification/DISKLESS_MANAGED_RF.md)

When diskless.managed.rf.enable=true, new diskless topics are created with
RF=rack_count using standard KRaft replica placement instead of legacy RF=1.

Changes:
- Compute RF from rack cardinality via rackCardinality()
- Use standard replicaPlacer.place() for rack-aware assignment
- Allow manual replica assignments when managed replicas enabled
- Add checkstyle suppression for extended createTopic method

Phase 1 limitations:
- Add Partitions inherits RF from existing partitions (Phase 3)
- Transformer not updated, uses legacy routing (Phase 2)
- Integration tests deferred to Phase 2
(See #478 docs/inkless/ts-unification/DISKLESS_MANAGED_RF.md)

Add three new controller metrics to track diskless topics:
- DisklessTopicCount: total number of diskless topics
- DisklessUnmanagedReplicasTopicCount: diskless topics with RF=1
- DisklessManagedReplicasTopicCount: diskless topics with RF>1

These metrics update in real-time via delta processing, not just on
snapshot load. For deleted topics, the diskless status is correctly
looked up from prevImage since the config is already removed from
newImage at that point.

Also adds docker-compose overlay for testing managed replicas with
3 brokers across 3 availability zones.