RBAC: allow listing permissions on the root folder (#82184)

* allow returning AC metadata for the root folder

* add a test

* share the reserved root folder UID with frontend

pkg/api/dtos/frontend_settings.go

@@ -235,6 +235,7 @@ type FrontendSettingsDTO struct {
 	SamlName                string                             `json:"samlName"`
 	TokenExpirationDayLimit int                                `json:"tokenExpirationDayLimit"`
 	SharedWithMeFolderUID   string                             `json:"sharedWithMeFolderUID"`
+	RootFolderUID           string                             `json:"rootFolderUID"`
 
 	GeomapDefaultBaseLayerConfig *map[string]any `json:"geomapDefaultBaseLayerConfig,omitempty"`
 	GeomapDisableCustomBaseLayer bool            `json:"geomapDisableCustomBaseLayer"`