Function protocol_apis_md 

pub fn protocol_apis_md() -> String

Protocol API catalog: every Kafka API key the broker advertises to a client.

The set is the one a client listener advertises with a client-metrics receiver configured. That is the widest client-facing surface: it leaves out the inter-broker-only keys, which no Kafka client sends, and it keeps the two KIP-714 telemetry keys, which a broker withholds only when an operator configures no receiver.