Add docker-compose example with HAProxy SNI router
Turnkey deployment: HAProxy on :443 peeks at the TLS SNI and routes
Telegram clients to mtg while forwarding everything else (including DPI
probes) to a real Caddy web server with automatic HTTPS.
This is the setup recommended in BEST_PRACTICES.md, packaged so that
operators can clone and run it with minimal configuration.
Refs: #458
dolonet