Feature request: add flag to control `force_upload` option in `sam sync`

### Describe your idea/feature/enhancement

I wish `sam sync` command took an optional flag `force_upload`. Currently if I make a minute change in one resource of the cloudformation stack, then all the packages are zipped and uploaded to s3 making the local loop slow. Although there is a cache mechanism it never gets triggered because the `force_upload` is hardcoded to `True`. Doing so on a forked version helped me remove 90+s per run (20%+ faster).

### Proposal

Add details of how to add this to the product.

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