Currently the storage_manager can be used outside of request context for some calls (eg. get), but not for others (eg. list). This is because it tries to automatically add a filter based on the current user in list, which of course fails if there's no user.
Instead, we can allow using the storage_manager with no request context, by simply not adding the filter if not called from a request handler.
This will allow easier using the storage_manager from code that doesn't run inside a request handler, eg. cluster validations/handlers, and in the future the admin CLI.