Update file turn_on_off.md with tips for proxies and firewalls with Duochat

What does this MR do and why?

Adding troubleshooting for basic network settings for DuoChat as based on customer experience here in ticket 5206395

Apache proxy settings can be found here.

After updating the proxy settings customer was able to access Duo chat via IDE, where they could not before. See the last comments on ticket.

Since recent updates to Duo chat troubleshooting, this feels like a better place for this update.

See previous MR !154183 (comment 1925739728)