Display domain that notifications are coming from

Problem/Motivation

If you use config notify with many projects and even just different environments when the notifications get sent to the same slack channel or from the same email address it can be tricky to work out which site the notifications have come from.

Steps to reproduce

1. Setup the module locally
2. Make a config change
3. Run cron or sent test
4. Do the same from a staging or live environments

The data of what has changed might be different but it does not always indicate from which environment the notification came from.
The email address that it sends from could be the same, and the notification could be going into the same slack channel.
There are some ways around this such as configuring config settings to different email/slack channels but it does still allow for mistakes or requires extra config that is not always necessary.

Proposed resolution

A new flag to be added into the settings for config notify that will be disabled by default that can add the full domain into the notification if checked.
This would change the message sent to include the domain it is being sent from.