Add traefik config files

https://github.com/chatmail/relay/pull/614#discussion_r2269887232

docker/files/entrypoint.sh

@@ -4,10 +4,12 @@ set -eo pipefail
 if [ "${USE_FOREIGN_CERT_MANAGER,,}" == "true" ]; then
     if [ ! -f "$PATH_TO_SSL_CONTAINER/fullchain" ]; then
         echo "Error: file '$PATH_TO_SSL_CONTAINER/fullchain' does not exist. Exiting..." > /dev/stderr
+        sleep 2
         exit 1
     fi
     if [ ! -f "$PATH_TO_SSL_CONTAINER/privkey" ]; then
         echo "Error: file '$PATH_TO_SSL_CONTAINER/privkey' does not exist. Exiting..." > /dev/stderr
+        sleep 2
         exit 1
     fi
 fi