refactor: bring metrics to http output (#3247)

* refactor: bring metrics to http output

* chore: remove unwrap

* chore: make walk plan accumulate

* chore: change field name and comment

* chore: add metrics to http resp header

* chore: move PrometheusJsonResponse to a separate file and impl IntoResponse

* chore: put metrics in prometheus resp header too

src/datanode/src/region_server.rs

@@ -655,7 +655,7 @@ impl RegionServerInner {
             Output::AffectedRows(_) | Output::RecordBatches(_) => {
                 UnsupportedOutputSnafu { expected: "stream" }.fail()
             }
-            Output::Stream(stream) => Ok(stream),
+            Output::Stream(stream, _) => Ok(stream),
         }
     }