feat: add TopicStat (#268)

* feat: add `TopicStat`

* chore: generate code

proto/greptime/v1/meta/heartbeat.proto

@@ -54,6 +54,8 @@ message HeartbeatRequest {
     FrontendWorkloads frontend = 11;
     FlownodeWorkloads flownode = 12;
   }
+  // The topic stats of the datanode.
+  repeated TopicStat topic_stats = 13;
 }
 
 /// The workload types of the datanode.
@@ -110,6 +112,17 @@ message RegionStat {
   map<string, bytes> extensions = 99;
 }
 
+message TopicStat {
+  // The topic name
+  string topic_name = 1;
+  // The total record size appended to topic since the datanode started.
+  uint64 record_size = 2;
+  // The total record number appended to topic since the datanode started.
+  uint64 record_num = 3;
+  // The latest entry id of the topic.
+  uint64 latest_entry_id = 4;
+}
+
 message FlowStat {
   // Each flow's in mem state's size in bytes
   // due to protobuf's key can't be a message, so we use uint32 as the key which