// HeartbeatRequest issues a heartbeat for a member in a group, ensuring that
// Kafka does not expire the member from the group.
HeartbeatRequest => key 12, max version 4, flexible v4+, group coordinator
  // Group is the group ID this heartbeat is for.
  Group: string
  // Generation is the group generation this heartbeat is for.
  Generation: int32
  // MemberID is the member ID this member is for.
  MemberID: string
  // InstanceID is the instance ID of this member in the group (KIP-345).
  InstanceID: nullable-string // v3+

// HeartbeatResponse is returned from a HeartbeatRequest.
HeartbeatResponse =>
  ThrottleMillis(2) // v1+
  // ErrorCode is the error for the heartbeat request.
  //
  // GROUP_AUTHORIZATION_FAILED is returned if the client is not authorized
  // to the group (no read perms).
  //
  // INVALID_GROUP_ID is returned in the requested group ID is invalid.
  //
  // COORDINATOR_NOT_AVAILABLE is returned if the coordinator is not available
  // (due to the requested broker shutting down or it has not completed startup).
  //
  // NOT_COORDINATOR is returned if the requested broker is not the coordinator
  // for the requested group.
  //
  // UNKNOWN_MEMBER_ID is returned if the member ID is not a part of the group,
  // or if the group is empty or dead.
  //
  // ILLEGAL_GENERATION is returned if the request's generation ID is invalid.
  //
  // REBALANCE_IN_PROGRESS is returned if the group is currently rebalancing.
  ErrorCode: int16