minor #12125 add FallbackResource alternative for assets/bundles in nginx (fliespl)

This PR was submitted for the master branch but it was merged into the 4.3 branch instead (closes #12125).

Discussion
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add FallbackResource alternative for assets/bundles in nginx

As described above - this location rule provides similar functionality to apache FallbackResource example.

Commits
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8958f6c add FallbackResource alternative for assets/bundles in nginx

Author: javiereguiluz

setup/web_server_configuration.rst

@@ -294,6 +294,13 @@ The **minimum configuration** to get your application running under Nginx is:
             # try to serve file directly, fallback to index.php
             try_files $uri /index.php$is_args$args;
         }
+        
+        # optionally disable falling back to php script for the asset directories
+        # which will allow nginx to return a 404 error when files are
+        # not found instead of passing the request to Symfony
+        location /bundles {
+            try_files $uri $uri/ =404;
+        }
 
         location ~ ^/index\.php(/|$) {
             fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;