archwiki: update the cache in the background

roles/archwiki/templates/nginx.d.conf.j2

@@ -88,6 +88,9 @@ server {
 
         fastcgi_cache wiki;
         fastcgi_cache_valid 200 10m;
+        fastcgi_cache_background_update on;
+        fastcgi_cache_use_stale updating;
+        fastcgi_cache_lock on;
 
         add_header X-Cache $upstream_cache_status;
     }
@@ -113,6 +116,10 @@ server {
         include        fastcgi.conf;
 
         fastcgi_cache wiki;
+        fastcgi_cache_background_update on;
+        fastcgi_cache_use_stale updating;
+        fastcgi_cache_lock on;
+
         add_header X-Cache $upstream_cache_status;
 
         limit_req zone=archwikilimit burst=10 nodelay;