Add docker-compose certbot configurations with backward compatibility (#6702)

Co-authored-by: Your Name <you@example.com>

docker/nginx/conf.d/default.conf.template

@@ -29,6 +29,9 @@ server {
       include proxy.conf;
     }
 
+    # placeholder for acme challenge location
+    ${ACME_CHALLENGE_LOCATION}
+
     # placeholder for https config defined in https.conf.template
     ${HTTPS_CONFIG}
 }