Support creating a tarball of existing objects from ceph like s3tar

[grapemix]

I just realize AWS release s3tar(https://github.com/awslabs/amazon-s3-tar-tool) which create a tarball of existing objects in Amazon S3. This feature would be handy for millions of tiny files like logs, WALs use case. It sounds like this feature would need works both from backend(ceph) and clients(s5cmd). Does anyone has better ideas?