KIP-153 — Include only client traffic in BytesOutPerSec metric

Accepted Kafka 1.0 MetricsBroker

Adds `ReplicationBytesInPerSec` and `ReplicationBytesOutPerSec` metrics to the broker, and changes `BytesOutPerSec` to exclude inter-broker replication traffic (counting only client consumer bytes). The existing `BytesOutPerSec` mixes consumer client traffic with follower replication traffic, making it impossible to measure actual client-facing egress bandwidth.

Details