I went ahead and wrote a blog post on how to get notified in Slack when new App store review comes in. I am not sure why the "domain" is not allowed to be included on this forum, but if you'd like to find it, the article is on Medium with the title: iOS App Store Reviews — Email or Slack Notifications.

Looks like the App Connect app (released by Apple) offers notifications when reviews come in.

Can't believe something as critical as this is not currently provided as functionality for iOS App Developers.