Add uwsgi caching to archweb

Cache urls which urls marks as can be cached by nginx. This offloads our
uwsgi workers and allows for speedier delivery of RSS feeds and other
cached routes.

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

@@ -2,6 +2,9 @@
 limit_req_zone $binary_remote_addr zone=rsslimit:8m rate=1r/m;
 limit_req_status 429;
 
+uwsgi_cache_path /var/lib/nginx/cache levels=1:2 keys_zone=archwebcache:10m inactive=60m;
+uwsgi_cache_key "$scheme$host$request_uri";
+
 upstream archweb {
     server unix:///run/uwsgi/archweb.sock;
 }
@@ -178,6 +181,10 @@ server {
         include uwsgi_params;
         uwsgi_pass archweb;
 
+        uwsgi_cache archwebcache;
+        uwsgi_cache_revalidate on;
+        add_header X-Cache-Status $upstream_cache_status;
+
         limit_req zone=rsslimit burst=10 nodelay;
     }
 
@@ -185,5 +192,9 @@ server {
         access_log   /var/log/nginx/{{ archweb_domain }}/access.log main;
         include uwsgi_params;
         uwsgi_pass archweb;
+
+        uwsgi_cache archwebcache;
+        uwsgi_cache_revalidate on;
+        add_header X-Cache-Status $upstream_cache_status;
     }
 }