Update guild vanity

curl --request POST \
  --url https://api.fluxer.app/v1/admin/guilds/update-vanity \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "guild_id": "<string>",
  "vanity_url_code": "<string>"
}
'

{
  "guild": {
    "id": "<string>",
    "name": "<string>",
    "features": [
      "<string>"
    ],
    "owner_id": "<string>",
    "icon": "<string>",
    "banner": "<string>",
    "member_count": 1073741823
  }
}