docs, stacks: Caddyfiles moved to a folder mount (conf/Caddyfile)

stacks/platform/caddy/docker-compose.yaml

@@ -6,7 +6,7 @@ services:
     ports:
       - "${HTTPS_PORT}:443"
     volumes:
-      - ./Caddyfile:/etc/caddy/Caddyfile
+      - ./conf:/etc/caddy:ro
       - /path/to/caddy/caddy_data:/data
       - /path/to/caddy/caddy_config:/config
       - /etc/caddy/certs:/etc/caddy/certs