Sub-processor change notifications and subscriptions in the Trust Center

As a Trust Center admin, I want visitors and customers to subscribe to our sub-processor list and be notified automatically when it changes, so we can meet our GDPR Art. 28 notification obligations without emailing customers manually.

What would help:
- "Subscribe to sub-processor updates" on the Trust Center's Subprocessors section
- When we add, remove or replace a sub-processor, subscribers get an email with what changed (name, purpose, location, effective date)
- Optional advance notice period (e.g. 30 days before the change takes effect)
- Change history / previous versions of the list - Log of who was notified and when, as evidence for audits Context: a customer raised this while comparing Trust Center platforms (alongside sending an updated sub-processor list to customers when changes are made).