convert / build: add networking support through network-manager flag

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

templates/debian.Dockerfile

@@ -17,3 +17,26 @@ RUN DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
 RUN systemctl preset-all
 
 RUN echo "root:{{- if .Password}}{{ .Password}}{{- else}}root{{- end}}" | chpasswd
+
+{{ if eq .NetworkManager "netplan" }}
+RUN apt install -y netplan.io
+RUN mkdir -p /etc/netplan && printf '\
+network:\n\
+  version: 2\n\
+  renderer: networkd\n\
+  ethernets:\n\
+    eth0:\n\
+      dhcp4: true\n\
+      nameservers:\n\
+        addresses:\n\
+        - 8.8.8.8\n\
+        - 8.8.4.4\n\
+' > /etc/netplan/00-netcfg.yaml \
+{{ else if eq .NetworkManager "ifupdown"}}
+RUN apt install -y ifupdown2
+RUN mkdir -p /etc/network && printf '\
+auto eth0\n\
+allow-hotplug eth0\n\
+iface eth0 inet dhcp\n\
+' > /etc/network/interfaces
+{{ end }}