Feature request: Reproducible ZIP packages

### Describe your idea/feature/enhancement

For verification/auditing purposes, it is quite nice to have reproducible SAM zip packages.

### Proposal

We will need to sort the files here in a predictable way before adding them to the zip.

https://github.com/aws/aws-sam-cli/blob/ee23953806be066ebfb72dd42e188de4866483ae/samcli/lib/package/utils.py#L241-L242

Also, we should reset the timestamps to epoch.

Things to consider:
1. Will this require any updates to the [SAM Spec](https://github.com/awslabs/serverless-application-model) - No
2. Will do this after https://github.com/aws/aws-sam-cli/pull/4644 is merged in.

### Additional Details

I don't mind doing this myself. Semi-related to #4622.