Split postcopy into a separate file. Introduce a head page "features.rst"
to keep all the features on top of migration framework.
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/r/20240109064628.595453-7-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Peter Xu