CDAP-17981: Introduce FileFetcherInternalHttpHandler in AppFabric
This is intended to be used for appfab to proxy files from distributed
file system, since it is possible that other services may not have
direct access to the distributed file system (e.g. in k8s where we
may want to run user code in isolated pods which don't have permission
to access distributed file system that appfab has access to)
