S3: Offer a ManagedUpload (multipart upload) implementation

[danopia]

Looking at s3.upload(), that specific function is implemented by the AWS.S3.ManagedUpload class. It appears to chop your stream into individual 5MB segments and upload them with a Multipart Upload strategy. This is actually separate from streaming request bodies because each 'part' is buffered. So I will track managed/multipart uploads in a separate issue 😅

Originally posted by @danopia in https://github.com/cloudydeno/deno-aws_api/issues/24#issuecomment-1084962149