I confirm that python3-edgegrid is a valid requirement for designate, this dependency has been added during Ussuri cycle. Note that python3-edgegrid 1.1.1 is provided by RDO (https://trunk.rdoproject.org/centos8/deps/latest/SRPMS/python-edgegrid-1.1.1-6.el8.src.rpm)
python-edgegrid-1.1.1-6.el8ost is availalbe