first class support for CI

**Is your feature request related to a problem? Please describe.**
It seems to me that aws-amplify did a great job in creating, manage and sharing cloud environments but when it comes to CI/CD process, it can be better.
the documentation has only a small area that mentions the headless scripts, which I found complex and also require external tooling for mocking the user manual steps in the setup process.

**Describe the solution you'd like**
Support for CI. as we store all the needed files in SCM we can add another file for CI with all the configs. most of the cli tools that I know that aim for CI knows how to fetch data from env vars or config files.

**Describe alternatives you've considered**
using the headless files. here again not sure what to use and in what order.
for example, I've aws creds as env vars, should I run aws_init.sh?