Refactor support ticket into a template

This is the same thing we do for go live requests and branding requests.

It’s easier to do templating logic in a templating language than in
Python.

app/templates/support-tickets/support-ticket.txt

@@ -0,0 +1,5 @@
+{{ content }}
+{% if current_service -%}
+Service: "{{ current_service.name }}"
+{{ url_for('main.service_dashboard', service_id=current_service.id) }}
+{% endif %}