Support global custom headers in NGINX

roles/nginx/templates/config/snippets/site-common.conf

@@ -26,6 +26,10 @@ limit_req zone=perserver burst={{ nginx_limit_perserver_burst }};
 # Enable HSTS.
 add_header Strict-Transport-Security "max-age=31556926" always;
 
+{% for hdr, value in nginx_global_custom_headers | default({}) | dictsort %}
+add_header {{ hdr }} "{{ value }}" always;
+{% endfor %}
+
 # Serve our favicon.
 location = /favicon.ico {
         expires 15d;