Update nginx configuration to revalidate if feature flags are up to date (#1107)

Co-authored-by: Copilot <[email protected]>

Author: romanowska

web_ui/nginx.conf

@@ -57,6 +57,7 @@ http {
         location /api/v1/feature_flags {
             alias /usr/share/nginx/flags/feature-flags.json;
             add_header Content-Type application/json;
+            add_header Cache-Control "no-cache, must-revalidate";
         }
     }
 }