feat: docker and versioning stuff

docker-compose.yml

@@ -1,14 +1,15 @@
 services:
   portfolio:
-    image: docker.lechner-systems.at/lechnersystems/maintenance:${IMAGE_TAG}
+    image: docker.lechner-systems.at/lechnersystems/maintenance:${IMAGE_TAG:-latest}
     build:
       context: .
       dockerfile: Dockerfile
     restart: unless-stopped
     env_file:
-      - .env
+      - path: .env
+        required: false
     dns:
       - 192.168.100.2
       - 192.168.100.6
     ports:
-      - ${MAIN_PORT}:80
+      - "${MAIN_PORT:-8080}:80"