Allow setting webhook name color and editing webhook messages

[advaith1]

It would be useful if we could set the name color of a webhook message instead of it always being white (like how it would look if it had a role), just like how we can set the username and avatar URL in the post request.

Also, it would be useful if we could edit webhook messages after sending them.

Mason said it would be fine to put both of these in one issue.

[andyearnshaw]

One of the things my bot uses webhooks for is mirroring a very basic in-game guild chat in a channel on Discord. It lets me reuse the avatars, specify the name, etc. The only downside is that every person is tagged as BOT, so it would be nice to change the text and the background colour of that tag too.

[advaith1]

unfortunately, Mason said that's probably not happening

[matmen]

thanks