Chore: Improve err message for notifications (#18757)

Improve message of notification json error
Fix test after change error message

pkg/services/alerting/rule.go

@@ -141,7 +141,7 @@ func NewRuleFromDBAlert(ruleDef *models.Alert) (*Rule, error) {
 		} else {
 			uid, err := jsonModel.Get("uid").String()
 			if err != nil {
-				return nil, ValidationError{Reason: "Neither id nor uid is specified, " + err.Error(), DashboardID: model.DashboardID, AlertID: model.ID, PanelID: model.PanelID}
+				return nil, ValidationError{Reason: "Neither id nor uid is specified in 'notifications' block, " + err.Error(), DashboardID: model.DashboardID, AlertID: model.ID, PanelID: model.PanelID}
 			}
 			model.Notifications = append(model.Notifications, uid)
 		}

pkg/services/alerting/rule_test.go

@@ -179,7 +179,7 @@ func TestAlertRuleModel(t *testing.T) {
 
 			_, err := NewRuleFromDBAlert(alert)
 			So(err, ShouldNotBeNil)
-			So(err.Error(), ShouldEqual, "Alert validation error: Neither id nor uid is specified, type assertion to string failed AlertId: 1 PanelId: 1 DashboardId: 1")
+			So(err.Error(), ShouldEqual, "Alert validation error: Neither id nor uid is specified in 'notifications' block, type assertion to string failed AlertId: 1 PanelId: 1 DashboardId: 1")
 		})
 	})
 }