Add traefik config files

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

traefik/post-hook.sh

@@ -0,0 +1,12 @@
+CERTS_DIR=${CERTS_DIR:-"/data/letsencrypt/certs"}
+
+for dir in "$CERTS_DIR"/*/; do
+    cd "$dir"
+    if [ -f "certificate.crt" ]; then
+        ln -sf certificate.crt fullchain
+    fi
+    if [ -f "privatekey.key" ]; then
+        ln -sf privatekey.key privkey
+    fi
+    cd -
+done