Expose an S3 bucket prefix as a Rack application with streaming.
Specify an S3 URI to mount a bucket and optional prefix:
# config.ru
run Rack::S3.new("s3://my-bucket/assets")
or, with options:
# config.ru
run Rack::S3.new(bucket: "my-app", prefix: "assets", client: Aws::S3::Client.new(...))
It'll look for "index.html" files at the root, or at a url ending with a slash.