- Add OPENVPN_PROCESS_USER=root, PUID=0, PGID=0 to default .env
to prevent gluetun from injecting 'user' directive into target.ovpn
which causes 'Unrecognized option' errors on Debian
- Add ExecStartPre to remove stale /etc/openvpn/target.ovpn before start
- Fixes#12988