Export designs when creating a project export
Right now, the database model, nor the design repository are included in an export. Which means they would be lost.
Ideally we'd include the design repository in the export and when the model is included designs should be available again after an import
The existing LFS export and import classes will also need to be modified. See #11090 (comment 188616511)
Documentation should be updated https://docs.gitlab.com/ee/user/project/settings/import_export.html