This is important as we need this BT during creating new erp5-site and
we are only able to look for it in the bootstrap directory if we use
the function getBootstrapBusinessTemplateUrl from ERP5Site.

Installing all BM(s) together does disturb the dependency. It should
be only done after we have successfully applied layers and transferred
all BM to new format.

This is because some of the files for portal_transforms are installed as component documents
and the installation for portal_transforms sub-objects wouldn't be successfull until the
components are installed and registered.

bt5_config: constructTemplatePath should return None in case the path doesn't exist yet. Needed for cases where we are creating a new path_item object