Trigger notifications to domain managers when domains are unassigned via member domain management page

[rachidatecs]

Issue description

As a domain manager, I want to receive notifications when a domain manager is removed via the domain assignments page.

Acceptance criteria

• When a member is removed from a domain via the domain assignments page, notifications go out to the existing managers of that domain.
• Success and error handling
• update the code for removing a manager based on these two comments from the previous pr, adding a warning message and moving the code to utility/email_invitations.py

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 sent if the user is removed via the "Domain Assignments" page, as well (which appears for org model).

Links to other issues

• 🔄 Relates to Trigger notifications to domain managers when portfolio member is removed #3530