(AWS backup): (add direct backup resource support for S3 buckets)

### Describe the feature

Currently there's no API to add an S3 bucket to a backup resource. We can do it for DynamoDB such as
```
BackupResource.fromDynamoDbTable(table)
```
I'd like to have an equivalent for S3:
```
BackupResource.fromS3Bucket(bucket);
```
The only way for now is to add tags in S3 bucket and still need to manually add all S3 permissions to backup role, which is not ideal.

### Use Case

Adding an S3 bucket to a backup plan directly.

### Proposed Solution

Expose the `BackupResource.fromS3Bucket` API in CDK.

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2

### Environment details (OS name and version, etc.)

AL2012

Start by locating the existing BackupResource.fromDynamoDbTable entry point in the AWS CDK repository and reviewing how backup resources are represented. Done means the public BackupResource.fromS3Bucket API is available for S3 buckets and is covered by the relevant project tests.

Written by the indexing model from the issue text.