[GroupsOfName] - Group cannot be empty - meaning when archiving is happening, a default user should be set in empty group

[GroupsOfName] - Group cannot be empty - meaning when archiving is happening, a default user should be set in empty group

It is a concept idea.

Summary

Add a default setting in backend configuration in order to have a default user set in empty groupOfName. Also removing the non existing DN from the list when a user is removed.