Custom Username and Emoji

[umairali]

Please add the option to add custom username and emoji.

Customized Appearance

You can customize the name and icon of your Incoming Webhook in the Integration Settings section below.
However, you can override the displayed name by sending "username": "new-bot-name" in your JSON payload. You can also override the bot icon either with "icon_url": "https://slack.com/img/icons/app-57.png" or "icon_emoji": ":ghost:".

[Nielsvanpach]

Feel free to send a PR for this