fix(docs): Remove CADDY_INGRESS_NETWORKS env var requirement

Following some discussions in the support room, this env is best made
redundant. It is only recommended as a workaround for some scenarios
where Caddy fails to detect the ingress network.
However, Docker breaks this by appending prefixes to network names.

The other approach of:

```diff
services:
  caddy:
+   environment:
+     - CADDY_INGRESS_NETWORKS=proxy
networks:
  proxy:
+   name: proxy
```

Can be suggested, but probably not necessary to document.

See https://github.com/lucaslorentz/caddy-docker-proxy/issues/207
for further details

docs/public/deploying/docker-compose.with-caddy-labels.yml

@@ -8,8 +8,6 @@ services:
     ports:
       - 80:80
       - 443:443
-    environment:
-      - CADDY_INGRESS_NETWORKS=proxy
     networks:
       - proxy
     volumes: