build: Generate cloud-init seed ISO

cloud-init/user-data.template

@@ -0,0 +1,28 @@
+#cloud-config
+package_update: true
+package_upgrade: true
+snap:
+  commands:
+    00: snap refresh --hold=forever
+package_reboot_if_required: true
+packages:
+  - qemu-guest-agent
+  - yq
+  - cifs-utils
+
+runcmd:
+  - apt-get install -y linux-modules-extra-$(uname -r)
+  - sysctl -w net.ipv6.conf.all.disable_ipv6=1
+  - systemctl enable --now qemu-guest-agent.service
+
+disable_root: false
+users:
+  - name: root
+    hashed_passwd: __ROOT_HASHED_PASSWORD__
+    lock_passwd: false
+    shell: /bin/bash
+    ssh_authorized_keys:
+      - __PUBLIC_SSHKEY__
+ssh_authorized_keys:
+  - >
+    __PUBLIC_SSHKEY__