fix: CopyObject behavior on expanded zones (#9729)

CopyObject was not correctly figuring out the correct
destination object location and would end up creating
duplicate objects on two different zones, reproduced
by doing encryption based key rotation.

cmd/api-headers.go

@@ -112,7 +112,7 @@ func setObjectHeaders(w http.ResponseWriter, objInfo ObjectInfo, rs *HTTPRangeSp
 
 	// Set all other user defined metadata.
 	for k, v := range objInfo.UserDefined {
-		if strings.HasPrefix(k, ReservedMetadataPrefix) {
+		if strings.HasPrefix(strings.ToLower(k), ReservedMetadataPrefixLower) {
 			// Do not need to send any internal metadata
 			// values to client.
 			continue