Alerting: Add first Grafana reserved label grafana_folder (#50262)

* Alerting: Add first Grafana reserved label g_label

g_label holds the title of the folder container the alert. The intention of this label
is to use it as part of the new default notification policy groupBy.

* Add nil check on updateRule labels map

* Disable gocyclo lint on schedule.ruleRoutine

will remove later in a separate refactoring PR to reduce complexity.

* Address doc suggestions

* Update g_folder for rules in folder when folder title changes

* Remove global bus in FolderService

* Modify tests to fit new common g_folder label

* Add changelog entry

* Fix merge conflicts

* Switch GrafanaReservedLabelPrefix from `g_` to `grafana_`

pkg/services/ngalert/tests/util.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/grafana/grafana/pkg/api/routing"
+	busmock "github.com/grafana/grafana/pkg/bus/mock"
 	"github.com/grafana/grafana/pkg/infra/log"
 	acmock "github.com/grafana/grafana/pkg/services/accesscontrol/mock"
 	"github.com/grafana/grafana/pkg/services/dashboards"
@@ -54,14 +55,16 @@ func SetupTestEnv(t *testing.T, baseInterval time.Duration) (*ngalert.AlertNG, *
 		cfg, dashboardStore, nil,
 		features, folderPermissions, dashboardPermissions, ac,
 	)
+
+	bus := busmock.New()
 	folderService := dashboardservice.ProvideFolderService(
 		cfg, dashboardService, dashboardStore, nil,
-		features, folderPermissions, ac,
+		features, folderPermissions, ac, bus,
 	)
 
 	ng, err := ngalert.ProvideService(
 		cfg, nil, routing.NewRouteRegister(), sqlStore, nil, nil, nil, nil,
-		secretsService, nil, m, folderService, ac, &dashboards.FakeDashboardService{}, nil,
+		secretsService, nil, m, folderService, ac, &dashboards.FakeDashboardService{}, nil, bus,
 	)
 	require.NoError(t, err)
 	return ng, &store.DBstore{