Revert "app/vmselect/promql: remove metric name from results of certain rollup functions in order to be consistent with Prometheus"

This reverts commit e5202a4eae.

Reason for revert: the previous behavior for VictoriaMetrics is easier to understand and use by users -
functions, which don't change the meaning of the time series shouldn't drop metric name.

Now the following functions do not drop metric name:

* max_over_time
* min_over_time
* avg_over_time
* quantile_over_time
* geomean_over_time
* mode_over_time
* holt_winters
* predict_linear

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/674

app/vmselect/promql/exec_test.go

@@ -3634,6 +3634,7 @@ func TestExecSuccess(t *testing.T) {
 			Values:     []float64{7.8, 9.9, 11.9, 13.9, 15.9, 17.9},
 			Timestamps: timestampsExpected,
 		}
+		r.MetricName.MetricGroup = []byte("foobar")
 		resultExpected := []netstorage.Result{r}
 		f(q, resultExpected)
 	})

app/vmselect/promql/rollup.go

@@ -169,12 +169,20 @@ var rollupFuncsRemoveCounterResets = map[string]bool{
 }
 
 var rollupFuncsKeepMetricGroup = map[string]bool{
+	"holt_winters":          true,
+	"predict_linear":        true,
 	"default_rollup":        true,
+	"avg_over_time":         true,
+	"min_over_time":         true,
+	"max_over_time":         true,
+	"quantile_over_time":    true,
 	"rollup":                true,
+	"geomean_over_time":     true,
 	"hoeffding_bound_lower": true,
 	"hoeffding_bound_upper": true,
 	"first_over_time":       true,
 	"last_over_time":        true,
+	"mode_over_time":        true,
 }
 
 func getRollupAggrFuncNames(expr metricsql.Expr) ([]string, error) {