Split changelog auto-subscribes into options per channel

Currently, there is only the option to auto-subscribe new users no matter where they come from.

This has the unfortunate consequence of subscribing everyone who emails us, which goes into the support module.

These are users who have never seen any privacy policy or opt in to subscribing, so it would be great if you could split this option into:

1. Auto-subscribe new support users

2. Auto-subscribe new identified users (authenticated through the SDK, or logged in to the feature portal and interacts with posts)

Not sure if this is easy or not, but for now we cannot auto-subscribe all which is a drag.