Allow to disable local disk type of access

Since Pages can run in a fully remote type of access we should allow disabling disk access completely.

Maybe the simplest way to achieve that would be to specify -enable-disk=false, or switch to specifying an array of -allowed-paths=[] instead that would superseed -pages-root.

This would be needed to ensure that we fully disable a disk-type of accesses for cases where it is not needed, like CNG.

Proposal:

• Introduce -enable-disk, when false Pages will not need to scan the pages-root directory. However, a pages-root value is still needed for daemonizing into a jail or chroot.