Alerting: Set "value" with evalmatches in G Managed (#34075)

When, and currently only when using a classic condition, evaluation information is added (which is like the EvalMatches from dashboard alerting).

This is returned via the API and can be included in notifications by reading the `__value__` label attached `.Alerts` in the template. It is a string.

pkg/services/ngalert/state/manager.go

@@ -74,8 +74,9 @@ func (st *Manager) setNextState(alertRule *ngModels.AlertRule, result eval.Resul
 	currentState.LastEvaluationTime = result.EvaluatedAt
 	currentState.EvaluationDuration = result.EvaluationDuration
 	currentState.Results = append(currentState.Results, Evaluation{
-		EvaluationTime:  result.EvaluatedAt,
-		EvaluationState: result.State,
+		EvaluationTime:   result.EvaluatedAt,
+		EvaluationState:  result.State,
+		EvaluationString: result.EvaluationString,
 	})
 
 	st.Log.Debug("setting alert state", "uid", alertRule.UID)

pkg/services/ngalert/state/state.go

@@ -24,8 +24,9 @@ type State struct {
 }
 
 type Evaluation struct {
-	EvaluationTime  time.Time
-	EvaluationState eval.State
+	EvaluationTime   time.Time
+	EvaluationState  eval.State
+	EvaluationString string
 }
 
 func resultNormal(alertState *State, result eval.Result) *State {