Feature request: Customize the questions and flow in sam init

### Describe your idea/feature/enhancement

It would be very useful to be able to customize the options presented to users when they run "sam init". This would allow us to have "sam init" present a list of customized getting started templates that are customized to our environment. This would provide an even more effective on-ramp for our developers.

### Proposal

I would think that it could be done similar to how you can customize the questions presented in the sam pipelines command, by providing a questions.json file or something similar that would change the behavior.

Things to consider:
1. Will this require any updates to the [SAM Spec](https://github.com/awslabs/serverless-application-model)

### Additional Details