Upgrade from 2 -> 3 can migrate user email addresses that Nexus Repository 3 considers not valid

While testing NEXUS-28454 I noticed that in nxrm2 we allowed users to have email addresses such as test@somewhere (note the lack of a .com or .net, etc.) but we don't allow that in nxrm3, so after migration when editing a user, you can be immediately shown a validation error on the users email address.

It seems we should change nxrm3 to allow same email structures that nxrm2 supports