Split CloudFormation support into a separate tool

[benkehoe]

It's a bunch of code and has additional dependencies, and the macro bit too...there's no good reason it should be in the main tool. #104 impacted the ability to install aws-sso-util at all for a dependency only used by the CloudFormation part.

Also probably consider making aws-sso-lib it's own repo as well?

[iainelder]

A split might make make it easier to use and maintain each tool. One can be used independently of the other.

The macro README says that the it could be a SAR app. I'd like that option for simpler deployment however the code is organized. In that way I believe I could enable the macro simply with a SAR resource in a template instead of custom scripting around the the SAM CLI.