We need to make sure the director undercloud backup/restore procedure is documented for osp-d 8.

Here is the documentation for 7:
https://access.redhat.com/documentation/en/red-hat-enterprise-linux-openstack-platform/version-7/back-up-and-restore-red-hat-enterprise-linux-openstack-platform/

I tested out those steps on an osp-d 8 undercloud, and the steps themselves still work with no changes needed.

I would only recommend switching steps 7 and 8 to improve usability. As step 8 is meant to be executed as the root user, but in step 7, we have told the user to switch to the stack user. So, it makes sense to do those steps in the opposite order.

Also in the existing step 7, we say:
sudo yum install -y python-rdomanager-oscplugin

That will still work in osp-d 8, but the package has been renamed to python-tripleoclient, so it would be more correct to say:
sudo yum install -y python-tripleoclient