Add support for creative discovery

[Luc1412]

POST https://fn-service-discovery-live-public.ogs.live.on.epicgames.com/api/v1/discovery/surface/{client_id}?appId=Fortnite

{
    "surfaceName": "CreativeDiscoverySurface_Frontend",
    "revision": -1,
    "partyMemberIds": ["ID"],
    "matchmakingRegion": ""
}

This returns the current discovery for the logged in player.