Allow webhooks to send stickers in the current guild

[advaith1]

Normal users and bots can send stickers that are in the current guild by sending the sticker_ids field. However, webhooks cannot send stickers, as the Execute Webhook endpoint does not have a sticker_ids field. This seems like an oversight since sticker_ids and message_reference are the only fields present in the Create Message endpoint but not the Execute Webhook endpoint, and there doesn't seem to be a reason to explicitly block webhooks from sending stickers. Webhooks are often used by bots for relaying user messages, so enabling webhook support would be useful to bots that do this.

[MinnDevelopment]

Seems like a rather annoying restriction of interactions to prevent sticker usage. This would encourage a bot to send messages using the POST endpoint on channels instead of the proper webhook way.