Better custom domain example

[kvinwang]

This PR replaces the previous custom-domain example with a more comprehensive, user-friendly version. The reverse proxy serves as an container that serves on HTTPS and directs traffic to your plain HTTP application server.

Example usage:

services:
  dstack-ingress:
    image: kvin/dstack-ingress@sha256:5cbf6eff9983fad4018de90ed11b0593c84f2022ddfc64b9eb513d1ba79970c7
    ports:
      - "443:443"
    environment:
      - DOMAIN=${DOMAIN}
      - GATEWAY_DOMAIN=${GATEWAY_DOMAIN}
      - CERTBOT_EMAIL=${CERTBOT_EMAIL}
      - CLOUDFLARE_API_TOKEN=${CLOUDFLARE_API_TOKEN}
      - SET_CAA=true
      - TARGET_ENDPOINT=http://app:80
    volumes:
      - /var/run/tappd.sock:/var/run/tappd.sock
      - cert-data:/etc/letsencrypt
    restart: unless-stopped
  app:
    image: nginx  # Replace with your application image
    restart: unless-stopped
volumes:
  cert-data:

Resolves Phala-Network/phala-cloud#21