Add option to open Dali+dafilesrv and add foreign file support

Allow an option to open up Dali+dafilesrv (to be secured by ingress/firewalls), so that bare-metal systems can access K8s HPCC DFS.
A dedicated dafilesrv (load-balanced) will be needed in the K8s environment to service the physical files.

This is a stop-gap until the DFS service supports the same mechanism in a similar way.