Allow admins to create default notifications settings to new members

This RFE is from a customer request to implement the ability of administrators to create templates of notifications to new members, as follow:

Current implementation
a) Select "Member" and assign rights (this already exists)
b) For the rights that have been selected all notifications are enabled by default

New behavior requested
a) Configure 3scale tenant to allow to change the default notification settings for all new members i.e. to "all off", "all off for billing", "all on for accounts", etc.
b) Select member and assign the rights
c) Notifications will be enabled based on the configuration performed under a