DirCopy copies or hardlinks the contents of one directory to another, properly
handling soft links, "security.capability" and (optionally) "trusted.overlay.opaque"
xattrs.
The copyOpaqueXattrs controls if "trusted.overlay.opaque" xattrs are copied.
Passing false disables copying "trusted.overlay.opaque" xattrs.
Mode indicates whether to use hardlink or copy content
const (
// Content creates a new file, and copies the content of the file Content Mode = iota// Hardlink creates a new hardlink to the existing file Hardlink
)