You have two possibilities, either to alter the samba/ldap catalog like you asked, or doing it with the old way, create a user and delegate its agenda
Resources really are just users. The paradigm in SOGo is to create a
special user for each resource and let the person in charge of that
resource know the password so that he/she can accept or deny events.
If many people are supposed to administrate the resource, you can allow
them to add or modify events, per type of event, on the resource's calendar.
Whenever a regular user needs that resource, he/she only needs to invite it. Source