Killing Floor 2 item server

The multiplayer game [Killing Floor 2](https://store.steampowered.com/app/232090/Killing_Floor_2/) (content warning: zombies, blood) needs to contact an item server to figure out which cosmetic items players of the game have collected. This item server is hosted on `analytics.tripwireinteractive.com`.

This domain needs to be whitelisted, otherwise players will get a "Failed To Reach Item Server" message in-game, and they won't be able to use the items they have collected in the past.