feat(s3-proxy): expose x-amz-restore to JS for Glacier rehydration

The catalog's archived/restore detection (parseRestoreHeader, isEffectivelyArchived)
reads the x-amz-restore HEAD response header to distinguish ongoing/expired
restores from cold-archived objects. The s3-proxy was hard-coding the
Access-Control-Expose-Headers list (and stripping S3's own) without including
x-amz-restore, so browsers received the header but JS couldn't read it —
rehydrated objects stayed showing 'Object Archived' instead of flipping to
'Restore in progress'. Add the header to the expose list.

Author: fiskus

s3-proxy/nginx.conf

@@ -38,7 +38,7 @@ http {
             add_header 'Access-Control-Allow-Methods' $http_access_control_request_method always;
             add_header 'Access-Control-Allow-Origin' '*' always;
             add_header 'Access-Control-Max-Age' '3000' always;
-            add_header 'Access-Control-Expose-Headers' 'Content-Length, Content-Range, ETag, x-amz-meta-helium, x-amz-bucket-region, x-amz-delete-marker, x-amz-request-id, x-amz-version-id, x-amz-storage-class' always;
+            add_header 'Access-Control-Expose-Headers' 'Content-Length, Content-Range, ETag, x-amz-meta-helium, x-amz-bucket-region, x-amz-delete-marker, x-amz-request-id, x-amz-version-id, x-amz-storage-class, x-amz-restore' always;
 
             # Return success on OPTIONS.
             if ($request_method = 'OPTIONS') {