Add notification integration with AWS chatbot

**Is your feature request related to a problem? Please describe.**

It will be very useful to monitor build status in Slack. AWS Chatbot makes it easy to integrate SNS to slack without having to create lambda functions.

**Describe the solution you'd like**

Have AWS Chatbot support events from amplify.

**Additional context**

Currently, we can listen for notifications using SNS and lambda. But having AWS Chatbot support the notification out of the box would make our life easier.

No files, tests, or entry points are named. Start by examining the existing SNS and Lambda notification path described in the issue, then determine how Amplify build events could reach AWS Chatbot without Lambda; done means AWS Chatbot can receive build-status notifications through the supported integration.

Written by the indexing model from the issue text.