// For KIP-500 / KIP-631, 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