Trigger notifications to domain managers when portfolio member is removed

[rachidatecs]

Issue description

As a domain manager, I want to receive notifications when a portfolio member is removed and loses access to assigned domains that I manage.

Acceptance criteria

• When a portfolio member is removed and loses access to previously assigned portfolio domains, the managers of those domains receive notifications
• Success and error handling

Additional context

This email is already being sent when a manager is removed via the "Domain Managers" page. So this ticket is to ensure that the email is also sent if the user is removed from a portfolio and loses access to domains.

Links to other issues

🔄 Relates to #3531