Extract sdk into its own lib

This had some side effects:

 - Have to add some utils from the kairos/machine modules, which IMHO
   should not be there, they should be here if the are generic enough
 - Dropping the sdk dir, just have the modules in the root dir

Signed-off-by: Itxaka <itxaka.garcia@spectrocloud.com>

clusterplugin/init.go

@@ -0,0 +1,9 @@
+package clusterplugin
+
+import "github.com/twpayne/go-vfs"
+
+var filesystem vfs.FS
+
+func init() {
+	filesystem = vfs.OSFS
+}