Revert "Remove location /healthz from nginx.conf.template"

This reverts commit 122f927.

Author: aaronskiba

nginx.conf.template

@@ -2,6 +2,11 @@ server {
   listen 8080;
   server_name _;
 
+  location /healthz {
+    access_log off;
+    return 200 "healthy\n";
+  }
+
   location ~ ^${RAILS_RELATIVE_URL_ROOT}/assets/ {
     alias /usr/share/nginx/html/assets/;
     expires 1y;