Add support for verifying file and directory permission on Windows

[kommendorkapten]

Initially discussed in this PR #347, see this comment #347 (comment) for more details.

That PR adds support for verifying that the permission mode for the metadata cache is a bit more restrictive, the "others" group can not read nor write any of the files, but it does not work on Windows.
Just a note, this functionality is not required by the TUF spec, but it is a nice to have feature.

[rdimitrov]

Closing since the code base changed and this is no longer valid. Do reopen if needed 👍

Thanks for raising this 👍