Alerting: Change __value__ label to __value_string__ annotation and add ValueString variable in notifications (#36032)

* Alerting: Allow __value__ label in notifications
was being removed by removePrivateItems
discoverd in #36020, but issue is not about that specifically

* __value__ label to __value_string__ annotation
and .ValueString extended property for notifications

pkg/services/ngalert/eval/eval.go

@@ -166,7 +166,7 @@ func executeCondition(ctx AlertExecCtx, c *models.Condition, now time.Time, data
 		return ExecutionResults{Error: err}
 	}
 
-	// eval captures for the '__value__' label.
+	// eval captures for the '__value_string__' annotation and the Value property of the API response.
 	captures := make([]NumberValueCapture, 0, len(execResp.Responses))
 
 	captureVal := func(refID string, labels data.Labels, value *float64) {

pkg/services/ngalert/notifier/channels/template_data.go

@@ -29,6 +29,7 @@ type ExtendedAlert struct {
 	SilenceURL   string      `json:"silenceURL"`
 	DashboardURL string      `json:"dashboardURL"`
 	PanelURL     string      `json:"panelURL"`
+	ValueString  string      `json:"valueString"`
 }
 
 type ExtendedAlerts []ExtendedAlert
@@ -87,6 +88,10 @@ func extendAlert(alert template.Alert, externalURL string, logger log.Logger) *E
 		}
 	}
 
+	if alert.Annotations != nil {
+		extended.ValueString = alert.Annotations[`__value_string__`]
+	}
+
 	matchers := make([]string, 0)
 	for key, value := range alert.Labels {
 		if !(strings.HasPrefix(key, "__") && strings.HasSuffix(key, "__")) {

pkg/services/ngalert/schedule/compat.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/go-openapi/strfmt"
+	"github.com/grafana/grafana-plugin-sdk-go/data"
 	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
 	"github.com/prometheus/alertmanager/api/v2/models"
 
@@ -29,8 +30,10 @@ func FromAlertStateToPostableAlerts(logger log.Logger, firingStates []*state.Sta
 	for _, alertState := range firingStates {
 		if alertState.NeedsSending(stateManager.ResendDelay) {
 			nL := alertState.Labels.Copy()
+			nA := data.Labels(alertState.Annotations).Copy()
+
 			if len(alertState.Results) > 0 {
-				nL["__value__"] = alertState.Results[0].EvaluationString
+				nA["__value_string__"] = alertState.Results[0].EvaluationString
 			}
 
 			genURL := appURL
@@ -42,7 +45,7 @@ func FromAlertStateToPostableAlerts(logger log.Logger, firingStates []*state.Sta
 			}
 
 			alerts.PostableAlerts = append(alerts.PostableAlerts, models.PostableAlert{
-				Annotations: alertState.Annotations,
+				Annotations: models.LabelSet(nA),
 				StartsAt:    strfmt.DateTime(alertState.StartsAt),
 				EndsAt:      strfmt.DateTime(alertState.EndsAt),
 				Alert: models.Alert{

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -1455,9 +1455,10 @@ var expNotifications = map[string][]string{
 			  },
 			  "annotations": {},
 			  "startsAt": "%s",
+        "valueString": "[ var='A' labels={} value=1 ]",
 			  "endsAt": "0001-01-01T00:00:00Z",
 			  "generatorURL": "http://localhost:3000/alerting/UID_WebhookAlert/edit",
-			  "fingerprint": "7611eef9e67f6e50",
+			  "fingerprint": "929467973978d053",
 			  "silenceURL": "http://localhost:3000/alerting/silence/new?alertmanager=grafana&matchers=alertname%%3DWebhookAlert",
 			  "dashboardURL": "",
 			  "panelURL": ""
@@ -1621,10 +1622,11 @@ var expNotifications = map[string][]string{
 		  {
 			"labels": {
 			  "__alert_rule_uid__": "UID_AlertmanagerAlert",
-              "__value__": "[ var='A' labels={} value=1 ]",
 			  "alertname": "AlertmanagerAlert"
 			},
-			"annotations": {},
+			"annotations": {
+        "__value_string__": "[ var='A' labels={} value=1 ]"
+      },
 			"startsAt": "%s",
 			"endsAt": "0001-01-01T00:00:00Z",
 			"generatorURL": "http://localhost:3000/alerting/UID_AlertmanagerAlert/edit",