Allow admin app to specify domain for registration email

This follows the pattern for invite emails where the admin app tells the
API which domain to use when generating the link.

This will starting working once the admin change is merged:
- [ ] TBC

It won’t break anything if it’s merged before the admin change.

app/user/rest.py

@@ -374,6 +374,8 @@ def send_user_confirm_new_email(user_id):
 
 @user_blueprint.route('/<uuid:user_id>/email-verification', methods=['POST'])
 def send_new_user_email_verification(user_id):
+    request_json = request.get_json()
+
     # when registering, we verify all users' email addresses using this function
     user_to_send_to = get_user_by_id(user_id=user_id)
 
@@ -387,7 +389,10 @@ def send_new_user_email_verification(user_id):
         service=service,
         personalisation={
             'name': user_to_send_to.name,
-            'url': _create_verification_url(user_to_send_to)
+            'url': _create_verification_url(
+                user_to_send_to,
+                base_url=request_json.get('admin_base_url'),
+            ),
         },
         notification_type=template.template_type,
         api_key_id=None,
@@ -556,10 +561,10 @@ def _create_reset_password_url(email, next_redirect, base_url=None):
     return full_url
 
 
-def _create_verification_url(user):
+def _create_verification_url(user, base_url):
     data = json.dumps({'user_id': str(user.id), 'email': user.email_address})
     url = '/verify-email/'
-    return url_with_token(data, url, current_app.config)
+    return url_with_token(data, url, current_app.config, base_url=base_url)
 
 
 def _create_confirmation_url(user, email_address):