cli command to transform sam template to regular cloudformation template?

### Describe your idea/feature/enhancement

I believe it could be useful to add a command to allow a user to see the cloudformation template produced after serverless transforms are applied.

### Proposal

`sam transform --template-file PATH --output-template-file PATH`

### Additional Details

A couple reasons I see value here:

1. education - for a new user, there's mystery around the effects of using sam syntax ... e.g. what policies are going to be automatically generated based on various properties i specify

2. some mechanisms in the wild are not yet friendly towards serverless transforms and being able to provide them with vanilla cloudformation, while still taking advantage of sam syntax during compose phase is a nice compromise