Auto-email to schools when designation request is actioned

**User Story**
As a ministry user, I want any schools to be notified _automatically_ when I approve or deny their designation request, so that I don't have to email them manually with each decision.

**Acceptance Criteria**
- [ ] Configure GC notify template which reads:
> "A designation request for your school has been completed. Please login to your school's account in the Student Information Management System to see more details"
- [ ] Trigger the e-mail to be sent once anytime a designation request for a school has been approved or declined
- Regardless of how many locations were included in the designation request, only send one e-mail

**Business ACs**
- [ ] Update training and documentation

No files or tests are named. Start by locating the designation-request approval and decline entry points, then inspect existing GC Notify integration and templates. Done means one notification is sent per school designation request decision, regardless of location count, with training and documentation updated.

Written by the indexing model from the issue text.