GIFT_CODE_UPDATE event not handled

Created by: Neuheit

Summary

I recently came across an unknown event from my bot logs:

Unknown event: GIFT_CODE_UPDATE
{
  "uses": 1,
  "sku_id": "521846918637420545",
  "code": "Mk5sW59364S6TqDr",
  "channel_id": "661971994480476160",
  "guild_id": "661971766125527070"
}

Doing some research, I found that it is intentionally not documented in discord docs, according to Jake, so we should decide whether to emit it or ignore it internally.