Alerting: added possibility to preview grafana managed alert rules. (#34600)

* starting to add eval logic.

* wip

* first version of test rule.

* reverted file.

* add info colum to result to show error or (with CC evalmatches)

* fix labels in evalmatch

* fix be test

* refactored using observables.

* moved widht/height div to outside panel rendere.

* adding docs api level.

* adding container styles to error div.

* increasing size of preview.

Co-authored-by: kyle <kyle@grafana.com>

pkg/expr/classic/reduce.go

@@ -24,6 +24,11 @@ func (cr classicReducer) ValidReduceFunc() bool {
 //nolint: gocyclo
 func (cr classicReducer) Reduce(series mathexp.Series) mathexp.Number {
 	num := mathexp.NewNumber("", nil)
+
+	if series.GetLabels() != nil {
+		num.SetLabels(series.GetLabels().Copy())
+	}
+
 	num.SetValue(nil)
 
 	if series.Len() == 0 {