SQL: Set errors as downstream based on underlying errorsource (#97192)

Set errors as downstream based on underlying errorsource

pkg/tsdb/grafana-postgresql-datasource/sqleng/sql_engine.go

@@ -235,6 +235,9 @@ func (e *DataSourceHandler) executeQuery(query backend.DataQuery, wg *sync.WaitG
 		emptyFrame.SetMeta(&data.FrameMeta{
 			ExecutedQueryString: query,
 		})
+		if backend.IsDownstreamError(err) {
+			source = backend.ErrorSourceDownstream
+		}
 		queryResult.dataResponse.Error = fmt.Errorf("%s: %w", frameErr, err)
 		queryResult.dataResponse.ErrorSource = source
 		queryResult.dataResponse.Frames = data.Frames{&emptyFrame}