CloudFormation: Use Sub instead of Join[Ref, GetAttr]

[jack1902]

Background

Description

The CloudFormation Templates should use Fn::Sub in place of Fn::Join with Fn::Ref and Fn::GetAttr as it makes for easier reading.

I believe making this change will make reading the CloudFormation Templates easier.

Documentation

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html

Desired Change

Use Fn::Sub as it is cleaner