fix: further ease the restriction of executing SQLs in new GRPC interface (#797)

* fix: carry not recordbatch result in FlightData, to allow executing SQLs other than selection in new GRPC interface

* Update src/datanode/src/instance/flight/stream.rs

Co-authored-by: Jiachun Feng <jiachun_feng@proton.me>

src/api/greptime/v1/database.proto

@@ -56,3 +56,7 @@ message ObjectResult {
 message FlightDataRaw {
   repeated bytes raw_data = 1;
 }
+
+message FlightDataExt {
+  uint32 affected_rows = 1;
+}