nginx: berlin: Cache Cuirass build products.

This should help further mitigate <https://issues.guix.gnu.org/64317>.

* hydra/nginx/berlin.scm (berlin-locations): Add location block for
"/download".

hydra/nginx/berlin.scm

@@ -173,6 +173,17 @@ PUBLISH-URL."
               "proxy_cache_valid any 10m;"
               "proxy_ignore_client_abort on;")))
 
+           (nginx-location-configuration
+            (uri "/download")                     ;Cuirass "build products"
+            (body
+             (list
+              "proxy_pass http://localhost:8081;"
+              "expires 10d;"                      ;override 'Cache-Control'
+              "proxy_cache static;"
+              "proxy_cache_valid 200 30d;"
+              "proxy_cache_valid any 10m;"
+              "proxy_ignore_client_abort on;")))
+
            (nginx-location-configuration          ;certbot
             (uri "/.well-known")
             (body (list "root /var/www;")))