feat: use byte sniffing

[Droid00000]

Summary

I understand that this is kinda out of the blue, and that this makes the code slightly more complex/approachable since you're dealing with file signatures and the like, but i have a kinda decent reason for wanting to change this

• Unfortunately, if we ever want to support stickers (specifically allowing them to be uploaded to servers), we need to provide the exact content type of the sticker file. Unlike every-other endpoint that accepts file uploads, the sticker endpoint is strict and rejects application/octet-stream or a content type that doesn't match the contents of a file.

• If you provide something like a Tempfile or StringIO to something like Server#create_emoji it's currently always fallback to a image/jpeg content type. While this is okay right now because Discord basically ignores the content-type your provide in the base64 string, they could decide to make it strict at anytime (like stickers). You could technically do something like below, to provide the content type, I think it's pretty janky to expect people to be defining singleton methods:

• If we ever decide to ditch rest-client, we won't be able to use the mime-types gem (unless we want to make it an explicit dependency) since it's a transitive dependency from rest-client.

• All of the file types that Discord supports are well-documented and easy to find: https://en.wikipedia.org/wiki/List_of_file_signatures

string_io.define_singleton_method(:original_filename) { "foo.#{my_extension}" }

Added

Discordrb.sniff_mime_type (thanks discord.py)

Fixed

I snuck in the doc fixes related to the component builder not being documented on a few interaction methods.