Add flatcar experimental example, another with coreos ignition

[afbjorklund]

This uses ignition and prefix, to support Flatcar Container Linux

It is the continuation of the original CoreOS, before Fedora CoreOS

Requirements:

• Add example for Fedora CoreOS, running ignition not cloud-init #1653
• Allow changing prefix for the installations #1655
• https://coreos.github.io/butane/ to be installed

Closes: #1372

See also https://www.flatcar.org/docs/latest/installing/vms/qemu/

[afbjorklund]

Almost forgot, it also needs a symlink created from the '/mnt` directory:

index 94c8973..1120d07 100644
--- a/pkg/cidata/cidata.TEMPLATE.d/ignition.yaml
+++ b/pkg/cidata/cidata.TEMPLATE.d/ignition.yaml
@@ -47,6 +47,20 @@ systemd:
         Where=/var/mnt/lima-cidata
         Options=ro,mode=0700,dmode=0700,overriderockperm,exec,uid=0
 
+        [Install]
+        RequiredBy=local-fs.target
+    # Note1: symlink required on flatcar
+    # Note2: it already exists in coreos
+    - name: mnt-lima-cidata.service
+      enabled: true
+      contents: |
+        [Unit]
+        Before=lima-ssh-ready.service lima-install-containerd.service lima-install-guestagent.service
+
+        [Service]
+        Type=oneshot
+        ExecStart=/bin/sh -c "test -d /mnt/lima-cidata || ln -s /var/mnt/lima-cidata /mnt/lima-cidata"
+
         [Install]
         RequiredBy=local-fs.target
     - name: lima-ssh-ready.service