When you want to invoke wg-quick yourself, for example from a script,
this procedure is useful to produce the configuration file for it.
* gnu/services/vpn.scm (define-module)<#:export>:
Add wireguard-configuration-file.
Change-Id: Ifab8a9d731de19d2943517bf18c156a56fea4cca
Signed-off-by: Nguyễn Gia Phong <cnx@loang.net>