KIP-500 (actually KIP-631): add BrokerRegistration and BrokerHeartbeat

The commit introducing these mentions KIP-500, but the description of
these requests is actually in KIP-631.

generate/definitions/62_broker_registration

@@ -0,0 +1,37 @@
+// For KIP-500, BrokerRegistrationRequest is an internal broker-to-broker only
+// request.
+BrokerRegistrationRequest => key 62, max version 0, flexible v0+
+  // The broker ID.
+  BrokerID: int32
+  // The cluster ID of the broker process.
+  ClusterID: uuid
+  // The incarnation ID of the broker process.
+  IncarnationID: uuid
+  // The listeners for this broker.
+  Listeners: [=>]
+    // The name of this endpoint.
+    Name: string
+    // The hostname.
+    Host: string
+    // The port.
+    Port: uint16
+    // The security protocol.
+    SecurityProtocol: int16
+  // Features on this broker.
+  Features: [=>]
+    // The name of the feature.
+    Name: string
+    // The minimum supported feature level.
+    MinSupportedVersion: int16
+    // The maximum supported feature level.
+    MaxSupportedVersion: int16
+  // The rack that this broker is in, if any.
+  Rack: nullable-string
+
+// BrokerRegistrationResponse is a response to a BrokerRegistrationRequest.
+BrokerRegistrationResponse =>
+  ThrottleMillis
+  // Any error code, or 0.
+  ErrorCode: int16
+  // The broker's assigned epoch, or -1 if none was assigned.
+  BrokerEpoch: int64(-1)

generate/definitions/63_broker_heartbeat

@@ -0,0 +1,25 @@
+// For KIP-500, BrokerHeartbeatRequest is an internal broker-to-broker only
+// request.
+BrokerHeartbeatRequest => key 63, max version 0, flexible v0+
+  // The broker ID.
+  BrokerID: int32
+  // The broker's epoch.
+  BrokerEpoch: int64(-1)
+  // The highest metadata offset that the broker has reached.
+  CurrentMetadataOffset: int64
+  // True if the broker wants to be fenced.
+  WantFence: bool
+  // True if the broker wants to be shutdown.
+  WantShutdown: bool
+
+// BrokerHeartbeatResponse is a response to a BrokerHeartbeatRequest.
+BrokerHeartbeatResponse =>
+  ThrottleMillis
+  // Any error code, or 0.
+  ErrorCode: int16
+  // True if the broker has approximately caught up with the latest metadata.
+  IsCaughtUp: bool
+  // True if the broker is fenced.
+  IsFenced: bool(true)
+  // True if the broker should proceed with its shutdown.
+  ShouldShutdown: bool