Add "headless mode" config

Closes https://git.autonomic.zone/coop-cloud/traefik/issues/24.

.env.sample

@@ -51,3 +51,6 @@ LOG_LEVEL=WARN
 
 ## Host-mode networking
 #COMPOSE_FILE="compose.yml:compose.host.yml"
+
+## "Headless mode" (no domain configured)
+#COMPOSE_FILE="compose.yml:compose.headless.yml"

compose.headless.yml

@@ -0,0 +1,14 @@
+---
+version: "3.8"
+
+services:
+  app:
+    deploy:
+      update_config:
+        failure_action: rollback
+        order: start-first
+      labels:
+        - "traefik.enable=true"
+        - "traefik.http.services.traefik.loadbalancer.server.port=web"
+        - "traefik.http.routers.traefik.entrypoints=web-secure"
+        - "traefik.http.routers.traefik.service=api@internal"