No way to add user to new emailList without unsubscribing them from existing subscription list

[quocdoancerebral]

The override is unsubscribing users from existing subscriptions and there's no way for us to grab an user's existing subscriptions to prevent them from being unsubscribed.

We need a way to add a user to a subscription without removing them from existing subscriptions. The current updateSubscriptions method does not allow that.