delete_stream fails in MinIO

[paraseba]

Running delete_stream against a MinIO deployment runs into

Missing required header for this request: Content-Md5.

Additional context

S3 API specification requires the presence of this header for all DeleteObjects requests to general purpose buckets:

The Content-MD5 request header is required for all Multi-Object Delete requests

AWS does in fact accept the request without the header, but object_store should include it for compatibility with the spec and other platforms.

[tustvold]

label_issue.py automatically added labels {'object-store'} from #5415