Do not store EvaluationString in Evaluation. (#44606) (#44795)

* do not store evaluation string in Evaluation.
* reduce number of buckets to store for a single state

(cherry picked from commit 984c95de63)

Co-authored-by: Yuriy Tseretyan <tceretian@gmail.com>

pkg/services/ngalert/api/api_prometheus.go

@@ -9,9 +9,9 @@ import (
 	"strings"
 	"time"
 
-	"github.com/grafana/grafana/pkg/services/ngalert/eval"
 	apiv1 "github.com/prometheus/client_golang/api/prometheus/v1"
 
+	"github.com/grafana/grafana/pkg/services/ngalert/eval"
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
 	"github.com/grafana/grafana/pkg/services/ngalert/store"
 
@@ -40,8 +40,8 @@ func (srv PrometheusSrv) RouteGetAlertStatuses(c *models.ReqContext) response.Re
 	for _, alertState := range srv.manager.GetAll(c.OrgId) {
 		startsAt := alertState.StartsAt
 		valString := ""
-		if len(alertState.Results) > 0 && alertState.State == eval.Alerting {
-			valString = alertState.Results[0].EvaluationString
+		if alertState.State == eval.Alerting {
+			valString = alertState.LastEvaluationString
 		}
 		alertResponse.Data.Alerts = append(alertResponse.Data.Alerts, &apimodels.Alert{
 			Labels:      map[string]string(alertState.Labels),
@@ -173,8 +173,8 @@ func (srv PrometheusSrv) RouteGetRuleStatuses(c *models.ReqContext) response.Res
 		for _, alertState := range srv.manager.GetStatesForRuleUID(c.OrgId, rule.UID) {
 			activeAt := alertState.StartsAt
 			valString := ""
-			if len(alertState.Results) > 0 && alertState.State == eval.Alerting {
-				valString = alertState.Results[0].EvaluationString
+			if alertState.State == eval.Alerting {
+				valString = alertState.LastEvaluationString
 			}
 			alert := &apimodels.Alert{
 				Labels:      map[string]string(alertState.Labels),