Add new custom build template for Docker ready image

Change-Id: I139f297948792ff8c83b15fac3ed2a55e163dc52
Signed-off-by: Dongjin Kim <tobetter@gmail.com>

custom/templates/docker/config

@@ -0,0 +1,7 @@
+BOARD=odroidn2plus
+ARCH=arm64
+DISTRO=focal
+FLAVOUR=server
+DEFAULT_USER=odroid
+DEFAULT_PASSWD=odroid
+ALLOW_ROOT_LOGIN=false

custom/templates/docker/fixups/S70-install-docker

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
+
+echo "deb [arch=arm64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
+
+apt update
+apt install -y --no-install-recommends \
+	docker-ce \
+	docker-ce-cli \
+	containerd.io
+
+usermod -aG docker @@DEFAULT_USER@@

custom/templates/docker/packages

@@ -0,0 +1,5 @@
+apt-transport-https
+ca-certificates
+curl
+gnupg
+lsb-release