`Content-Type: aws-chunked` is used on S3 PUT requests to signal SigV4
streaming uploads: the body is sent in AWS-formatted chunks, each
chunk framed and HMAC-signed.
When copying from a non S3 compatible object store (like Digital
Ocean) the objects can have `Content-Type: aws-chunked` (which you
won't see on AWS S3). Attempting to copy these objects to S3 with
`--metadata` this produces this error.
aws-chunked encoding is not supported when x-amz-content-sha256 UNSIGNED-PAYLOAD is supplied
This patch makes sure `aws-chunked` is removed from the `Content-Type`
metadata both on the way in and the way out.
Fixes#8724
cb1507fa96