S3 Object Storage Support

[abhemanyus]

Continuing from https://github.com/harlanc/xiu/issues/51#issuecomment-2317021418 @harlanc We don't need to put time-consuming I/O tasks on separate threads. If they are async, and we are running our entire application using an async runtime (like tokio), then all tasks will be non-blocking by default, and it will create new threads as necessary to handle parallel tasks. I am uploading the files to S3 to make a VOD archive. Since the S3 bucket will likely have some caching functionality, the index.m3u8 file, once created, will remain frozen in state even as it is updated. That is why I also want a small chunk of the livestream available from the livestreaming server itself.