[VictoriaFalls] Add a VFS yunq stub and register it.

sys/victoriafalls/victoriafalls_server.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <glacier/memory/unique_ptr.h>
+
+#include "victoriafalls/victoriafalls.yunq.server.h"
+
+class VFSServer : public VFSServerBase {
+ public:
+  static glcr::ErrorOr<glcr::UniquePtr<VFSServer>> Create();
+
+  glcr::ErrorCode HandleOpenFile(const OpenFileRequest&,
+                                 OpenFileResponse&) override;
+
+ private:
+  VFSServer(z_cap_t endpoint_cap) : VFSServerBase(endpoint_cap) {}
+};