End-to-end tests: Use a better mechanism to compare CloudFormation templates

[madeline-k]

The end-to-end tests currently use git diff to compare input and output CloudFormation templates. This is not sophisticated enough, because files of two templates may look different, even when the CloudFormation templates are equivalent.

A couple options to implement a more advance mechanism here:

1. Do JSON object comparison. We should also consider automatically resolving differences where the JSON is different, but the CloudFormation templates are equivalent.
2. Create a CloudFormation stack from the original template, then do a cdk diff with the new stack. This will have challenges with handling credentials if we want to do it in a pipeline or in GitHub actions.