rgw/restore: Update expiry-date of restored copies

rgw/restore: Update expiry-date of restored copies

As per AWS spec (https://docs.aws.amazon.com/AmazonS3/latest/API/API_RestoreObject.html),
if a `restore-object` request is re-issued on already restored copy, server needs to
update restoration period relative to the current time. These changes handles the same.

Note: this applies to only temporary restored copies

Signed-off-by: Soumya Koduri <skoduri@redhat.com>