Alerting: Display query from grafana-managed alert rules on /api/v1/rules (#45969)

* Aleting: Extract query from alerting rule model for api/v1/rules

* more changes and fixtures

* appease the linter

pkg/services/ngalert/models/alert_query.go

@@ -2,6 +2,7 @@ package models
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"time"
 
@@ -12,6 +13,8 @@ import (
 const defaultMaxDataPoints float64 = 43200 // 12 hours at 1sec interval
 const defaultIntervalMS float64 = 1000
 
+var ErrNoQuery = errors.New("no `expr` property in the query model")
+
 // Duration is a type used for marshalling durations.
 type Duration time.Duration
 
@@ -174,6 +177,28 @@ func (aq *AlertQuery) GetDatasource() (string, error) {
 	return aq.DatasourceUID, nil
 }
 
+// GetQuery returns the query defined by `expr` within the model.
+// Returns an ErrNoQuery if it is unable to find the query.
+// Returns an error if it is not able to cast the query to a string.
+func (aq *AlertQuery) GetQuery() (string, error) {
+	if aq.modelProps == nil {
+		err := aq.setModelProps()
+		if err != nil {
+			return "", err
+		}
+	}
+	query, ok := aq.modelProps["expr"]
+	if !ok {
+		return "", ErrNoQuery
+	}
+
+	q, ok := query.(string)
+	if !ok {
+		return "", fmt.Errorf("failed to cast query to string: %v", aq.modelProps["expr"])
+	}
+	return q, nil
+}
+
 func (aq *AlertQuery) GetModel() ([]byte, error) {
 	err := aq.setMaxDatapoints()
 	if err != nil {