Package delta file permission bits

[mudler]

The utils CopyFile (https://github.com/mudler/luet/blob/develop/pkg/helpers/file.go#L204) is used by the artifact generator when computing the Delta. It uses copy.Copy behind the scenes, but it needs to behave more or less the Docker equivalent we use while unpacking.

First, It needs to be disjointed from the helper as it is also used internally to copy data and have to be more generic supporting at least:

• sticky bits and additional perm bits
• xattrs( we do already )
• chown and preserve dir permissions (all parent dirs, we do now first level)