This PR adds a full configuration to setup a WhatsApp proxy with Traefik, expose similar ports to existing haproxy configuration, but with a much simpler setup process and more versatile configurations.

The main advantages over HAProxy include:

1. No more building process. only a compose file and traefik image from docker official image, minimize maintenance cost for project maintainers. (Resolves Suggestion: Create tag release along with the docker releases  #131)
2. Much simpler setup process for users. docker compose up -d is all we need.
3. Safer default settings. Using wildcard DNS for proxy access protect server from malicious scanners. The domain name defaults to whatsapp-<host-ip>.traefik.me but easy configurable, user can change to whatever-<host-ip>.other-wildcard-dns.provider even their own domain names.
   The domain name is essentially the password for accessing the proxy, while others can only see an empty 404 page, which resolves How to minimise the detection factors? #16, also resolves Using domain/sub-domain instead of an IP #120. The only server fingerprint is the default TLS certificate which only indicate it being a traefik server but not whatsapp proxy server. and it can also be further anonymized easily
   the server name setting can even be hot reloaded (a traefik feature😉)
4. Easier co-existance with other web services on same server, saving precious 80/443 ports. Traefik is a container-native edge router (a reverse proxy) which is much much simpler to manage than nginx/haproxy if all your services are running in docker.
5. One-click ACME setup. The necessary config blocks are provided as comments inside traefik.toml and whatsapp_proxy.toml. However the certificate is not very important because WhatsApp client does not verify this certificate, and medias are sent with TLS passthrough, the connection of which is already secure.

I'd recommend Traefik to be the default option for average users, but let it be an alternative for now 😉