add view link in message log for letter notifications

app/templates/views/api/index.html

@@ -71,6 +71,9 @@
               <dt>{{ key }}:</dt>
               <dd class="api-notifications-item-data-item">{{ notification[key] }}</dd>
             {% endfor %}
+            {% if notification['notification_type'] == 'letter' %}
+              <a href="{{ url_for('.view_notification', service_id=current_service.id, notification_id=notification.id) }}">View letter</a>
+            {% endif %}
           </dl>
         </div>
       </details>