Introducing a migration mode to both sides of the migration (send and
receive), so that a user can desribe which way the memory should be
migrated between the source and destination VMs.
For now, we only introduce `precopy` and `postcopy` as viable options,
but we can expect other modes (more optimized) to be added in the
future.
Signed-off-by: Sebastien Boeuf <sboeuf@meta.com>
Assisted-by: Claude:claude-opus-4-8