Prefix remote bucket with 's3'

[katxiao]

Problem Description

If the user supplies an S3 bucket, we should have them prefix the URL with "s3://"

Eg. "s3://sdv-demo-datasets"

Expected behavior

The following command should run the datasets in the sdv-demo-datasets s3 bucket.

benchmark_single_table(
    ...
    additional_datasets_folder='s3://sdv-demo-datasets',
)