When using the webhook, the previous method to edit a message was to
delete the old one via the classical API, and to create a new message
via the webhook. While this works, this means that editing "old" messages
lead to a mess where the chronological order is no longer respected.
This uses an hidden API explained in https://support.discord.com/hc/en-us/community/posts/360034557771
to achieve a proper edition using the webhook API.
The obvious downside of this approach is that since it is an
undocumented API for now, so there is no stability guarantee :/
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