fix: correct environment variable syntax in Caddyfile and clean up Docker Compose configuration

- Update Caddyfile to use correct syntax for environment variables in GoDaddy DNS settings
- Remove unnecessary version declaration from docker-compose.caddy.yml for clarity

docker-compose.caddy.yml

@@ -4,8 +4,6 @@
 # Starten: docker compose -f docker-compose.yml -f docker-compose.caddy.yml up -d
 # Stoppen: docker compose -f docker-compose.yml -f docker-compose.caddy.yml down
 
-version: '3.8'
-
 services:
   caddy:
     # Verwende Custom-Image mit GoDaddy DNS-Plugin