fix: make execute_webhook supports avatar

[yuto0214w]

1. It wasn't possible to edit webhook to change avatar, so edited it to use wh.avatar
2. This will override message.author.username if wh.name present

[braindigitalis]

This works, we should avoid calling json::parse on the object unless absolutely neccessary and you didnt have support for uploaded avatars:

	if (!thread_name.empty() || wh.image_data || !wh.avatar.empty() || !wh.name.empty()) { // only use json::parse if one of the optional parameters is set
		json j = json::parse(m.build_json(false));
		if (!thread_name.empty()) {
			j["thread_name"] = thread_name;
		}
		if (!wh.avatar.empty()) {
			j["avatar_url"] = wh.avatar;
		} else if (wh.image_data) {
			j["avatar_url"] = *image_data;
		}
		if (!wh.name.empty()) {
			j["username"] = wh.name;
		}
		body = j.dump();
	}

The formatting of your code is really odd and not in line with the coding style guide: https://dpp.dev/coding-standards.html

Please change your code to fit the style guide and implement the missing features as above, and i'd be happy to merge it in. :)

[yuto0214w]

Thanks for the feedback.
Fixed code style.
But for support of uploading avatar, as avatar_url only accepts http(s), it isn't possible to do like so other than modifying webhook.

[braindigitalis]

no pretty sure you can send a base64 encoded image in the image data, rather than a remote URL, same as when modifying webhook

[yuto0214w]

I tested dozen times, and read documentation but I couldn't seem to upload avatar without modifying webhook.
But as webhook avatar url format is https://cdn.discordapp.com/avatars/:id/:hash.png, I still don't think it's possible to do

[braindigitalis]

but those are user avatars, how do you get one uploaded to use it?