[aws-s3-deployment] support for empty folder deployement

### Description

With the following assets folder:

assets/
|----> FolderA/

Instantiate BucketDeployement has no effect.
```
new BucketDeployment(this, "DeployWebsite", {
sources: [Source.asset("./assets")],
destinationBucket: myBucket
}); // no effect
```
What would be expected?

A bucket with the following structure:

Mybucket:
|----> FolderA/

### Use Case

required to generate folder-level access bucket policies

### Proposed Solution

As a workaround, i use empty file to force BucketDeployement to render the folder structures
And delete the empty file afterwards

assets/
|----> FolderA/ ---->emptyFiles.txt

### Other

* [ ] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

---

This is a :rocket: Feature Request

Start by tracing the BucketDeployment construct and Source.asset handling in the aws-cdk repository. Check how assets are enumerated before deployment and identify where empty directories are discarded. Done means an assets folder containing only FolderA produces a corresponding FolderA/ structure in the destination bucket, with coverage for the behavior.

Written by the indexing model from the issue text.