feat: introduce node workloads (#235)

* feat: introduce node workloads

* feat: add feature gate

* chore: apply suggestions from CR

proto/greptime/v1/meta/common.proto

@@ -22,6 +22,7 @@ message RequestHeader {
   uint64 protocol_version = 1;
   // member_id is the ID of the sender server.
   uint64 member_id = 3;
+  // The role of the sender server.
   Role role = 4;
   // Encoded trace_id & span_id, follow the w3c Trace Context
   // https://www.w3.org/TR/trace-context/#header-name

proto/greptime/v1/meta/heartbeat.proto

@@ -48,6 +48,27 @@ message HeartbeatRequest {
   uint64 node_epoch = 7;
   NodeInfo info = 8;
   FlowStat flow_stat = 9;
+  /// The workloads of the node.
+  oneof node_workloads {
+    DatanodeWorkloads datanode = 10;
+    FrontendWorkloads frontend = 11;
+    FlownodeWorkloads flownode = 12;
+  }
+}
+
+/// The workload types of the datanode.
+message DatanodeWorkloads {
+  repeated int32 types = 1;
+}
+
+/// The workload types of the frontend.
+message FrontendWorkloads {
+  repeated int32 types = 1;
+}
+
+/// The workload types of the flownode.
+message FlownodeWorkloads {
+  repeated int32 types = 1;
 }
 
 enum RegionRole {