add https-squid

Additional settings are required when cache_peer only allows HTTPS. (ssl option)

Example:
```
cache_peer proxy.example.com parent 443 0 no-digest no-netdb-exchange connect-fail-limit=2 connect-timeout=8 round-robin no-query allow-miss proxy-only name=secure login=xxxx:yyy ssl ssldomain=xxx.example.com
```