Tell users that letters are coming

Users might be interested in letters. And when they’re fully
available, users will probably be able to control whether letters are
on/off for their service.

Until that point, the only way of getting the feature is to ask us. So
let’s make an in-the-meantime page that directs them to ask us, from the
place where they’d be able to do it themselves.

Wording TBC.

app/main/views/service_settings.py

@@ -286,6 +286,15 @@ def service_set_international_sms(service_id):
     )
 
 
+@main.route("/services/<service_id>/service-settings/set-letters", methods=['GET'])
+@login_required
+@user_has_permissions('manage_settings', admin_override=True)
+def service_set_letters(service_id):
+    return render_template(
+        'views/service-settings/set-letters.html',
+    )
+
+
 @main.route("/services/<service_id>/service-settings/set-letter-contact-block", methods=['GET', 'POST'])
 @login_required
 @user_has_permissions('manage_settings', admin_override=True)