* S3: Fix Content-Encoding header not preserved (#7894)
The Content-Encoding header was not being returned in S3 GET/HEAD responses
because it wasn't being stored in metadata during PUT operations.
Root cause: The putToFiler function only stored a hardcoded list of standard
HTTP headers (Cache-Control, Expires, Content-Disposition) but was missing
Content-Encoding and Content-Language.
Fix: Added Content-Encoding and Content-Language to the list of standard
headers that are stored in entry.Extended during PUT operations.
This matches the behavior of ParseS3Metadata (used for multipart uploads)
and ensures consistency across all S3 operations.
Fixes#7894
* Update s3api_object_handlers_put.go
