* s3api: stop echoing stored tags and internal attributes on GET/HEAD
setResponseHeaders copied every entry.Extended key into the response,
only filtering xattr- and x-seaweedfs-. Stored object tags
(X-Amz-Tagging-*) and the gateway's own attributes (Seaweed-X-Amz-Acl,
-Owner, -Version-Id, -Object-Lock-Mode, ...) therefore leaked to any
caller holding s3:GetObject, and to anonymous readers on public-read
objects, without s3:GetObjectTagging or READ_ACP.
Tag count, user metadata, storage class and the real S3 headers
(x-amz-version-id, x-amz-object-lock-*) are unaffected.
* s3api: match stored tag and internal attribute keys case-insensitively
