KIP-848: add ConsumerGroupHeartbeat proto

generate/definitions/68_consumer_group_heartbeat

@@ -0,0 +1,61 @@
+// ConsumerGroupHeartbeat is a part of KIP-848; there are a lot of details
+// to this request so documentation is left to the KIP itself.
+ConsumerGroupHeartbeatRequest => key 68, max version 0, flexible v0+
+  // The group ID.
+  Group: string
+  // The member ID generated by the coordinator. This must be kept during
+  // the entire lifetime of the member.
+  MemberID: string
+  // The current member epoch; 0 to join the group, -1 to leave, -2 to
+  // indicate that the static member will rejoin.
+  MemberEpoch: int32
+  // Instance ID of the member; null if not provided or if unchanging.
+  InstanceID: nullable-string
+  // The rack ID of the member; null if not provided or if unchanging.
+  RackID: nullable-string
+  // RebalanceTimeoutMillis is how long the coordinator will wait on a member
+  // to revoke its partitions. -1 if unchanging.
+  RebalanceTimeoutMillis: int32(-1)
+  // Subscribed topics; null if unchanging.
+  SubscribedTopicNames: nullable[string]
+  // The server side assignor to use; null if unchanging.
+  ServerAssignor: nullable-string
+  // Topic partitions owned by the member; null if unchanging.
+  Topics: nullable[=>]
+    // The topic ID.
+    TopicID: uuid
+    // The partitions.
+    Partitions: [int32]
+
+// ConsumerGroupHeartbeatResponse is returned from a ConsumerGroupHeartbeatRequest.
+ConsumerGroupHeartbeatResponse =>
+  ThrottleMillis
+  // ErrorCode is the error for this response.
+  //
+  // Supported errors:
+  // - GROUP_AUTHORIZATION_FAILED (version 0+)
+  // - NOT_COORDINATOR (version 0+)
+  // - COORDINATOR_NOT_AVAILABLE (version 0+)
+  // - COORDINATOR_LOAD_IN_PROGRESS (version 0+)
+  // - INVALID_REQUEST (version 0+)
+  // - UNKNOWN_MEMBER_ID (version 0+)
+  // - FENCED_MEMBER_EPOCH (version 0+)
+  // - UNSUPPORTED_ASSIGNOR (version 0+)
+  // - UNRELEASED_INSTANCE_ID (version 0+)
+  // - GROUP_MAX_SIZE_REACHED (version 0+)
+  ErrorCode: int16
+  // A supplementary message if this errored.
+  ErrorMessage: nullable-string
+  // The member ID generated by the coordinator; provided when joining
+  // with MemberEpoch=0.
+  MemberID: nullable-string
+  // The member epoch.
+  MemberEpoch: int32
+  // The heartbeat interval, in milliseconds.
+  HeartbeatIntervalMillis: int32
+  // The assignment; null if not provided.
+  Assignment: nullable=>
+    // The topics partitions that can be used immediately.
+    Topics: [=>]
+      TopicID: uuid
+      Partitions: [int32]