Fix serving of assets via nginx

Changes and notes provided by Shaun Bathgate:
•	^/dmp-pgd-staging/assets/(.*)$ captures everything after /assets/ into $1.
•	alias /usr/share/nginx/html/assets/; means Nginx maps $1 → /usr/share/nginx/html/assets/<$1>.
•	try_files $1 =404; ensures that if <filename> doesn’t exist, you get a 404 – and if it does exist, you get the file directly.

Author: aaronskiba

nginx.conf.template

@@ -7,11 +7,14 @@ server {
     return 200 "healthy\n";
   }
 
-  location ~ ^${RAILS_RELATIVE_URL_ROOT}/assets/ {
+  location ~ ^${RAILS_RELATIVE_URL_ROOT}/assets/(.*)$ {
     alias /usr/share/nginx/html/assets/;
     expires 1y;
     add_header Cache-Control "public, max-age=31536000, immutable";
     add_header X-Debug-Path $request_filename always;
+    # Let Nginx check /usr/share/nginx/html/assets/<captured-path>
+    # If missing, return 404
+    try_files $1 =404;
 
     add_header X-Frame-Options "DENY" always;
     add_header X-Content-Type-Options "nosniff" always;