www/caddy: Update docs for os-caddy-1.7.1 (opnsense#602)

* www/caddy: Update docs for os-caddy-1.7.1

* www/caddy: Add hint about duplicate domain:port combinations.

* www/caddy: Fix hint about multiple domains with same port.

* www/caddy: Abort is not a configurable option anymore and the default

* www/caddy: Correct the advanced configuration example

* www/caddy: Fix two typos

Author: Monviech