Make apt-cacher-ng a client of its own server (#4092)

Per https://askubuntu.com/questions/1503184/apt-cacher-ng-not-caching-packages-installed-on-the-server

Author: pgcudahy

install/apt-cacher-ng-install.sh

@@ -16,6 +16,9 @@ update_os
 msg_info "Installing Apt-Cacher NG"
 DEBIAN_FRONTEND=noninteractive $STD apt-get -o Dpkg::Options::="--force-confold" install -y apt-cacher-ng
 sed -i 's/# PassThroughPattern: .* # this would allow CONNECT to everything/PassThroughPattern: .*/' /etc/apt-cacher-ng/acng.conf
+cat << EOF >/etc/apt/apt.conf.d/00aptproxy.conf
+Acquire::http::Proxy "http://localhost:3142";
+EOF
 systemctl enable -q --now apt-cacher-ng
 msg_ok "Installed Apt-Cacher NG"