🔧 Add cache-control headers

Check static resources for modifications after 1 hour.
Never cache API responses.

Why:
- We are not yet using content hashed static resources, so we need to
  tell the browser to refresh its cache occasionally. Currently the
  users need to do a force refresh after deployment.

web/docker/nginx-default.conf.template

@@ -21,11 +21,15 @@ server {
   real_ip_recursive on;
 
   location / {
+    expires 1h;
+    add_header Cache-Control "public";
     root   /usr/share/nginx/html;
     try_files $uri /index.html;
   }
 
   location /api {
+    expires -1;
+    add_header Cache-Control "private";
     proxy_set_header Host $http_host;
     proxy_set_header X-Forwarded-Proto $scheme;
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;