Adding AWS CloudFormation Support

[ghost]

I plan to add AWS CloudFormation support to NixOps.

Reasons:

• CloudFormation is a well-tested tool for declaratively creating AWS resources
• Affords us full access to the range of AWS resources managed by CloudFormation
• CloudFormation documentation is well done

Once completed, this could also be done for CloudFormation's equivalents on GCP and Azure.

[o1lo01ol1o]

Is there any update on the status of CloudFormation in nixops?

[schlichtanders]

@LorenzoFernando any updates?