feat: add QueryContext to DdlTaskRequest and FlowRequestHeader (#166)

proto/greptime/v1/flow/server.proto

@@ -33,6 +33,14 @@ service Flow {
   rpc HandleMirrorRequest(InsertRequests) returns (FlowResponse);
 }
 
+message FlowRequestHeader {
+  // Encoded trace_id & span_id, follow the w3c Trace Context
+  // https://www.w3.org/TR/trace-context/#header-name
+  map<string, string> tracing_context = 1;
+  // The contextual information of the query
+  QueryContext query_context = 2;
+}
+
 message InsertRequests { repeated InsertRequest requests = 1; }
 
 message InsertRequest {
@@ -41,6 +49,7 @@ message InsertRequest {
 }
 
 message FlowRequest {
+  FlowRequestHeader header = 64;
   oneof body {
     CreateRequest create = 1;
     DropRequest drop = 2;