MigrationProcess: StorageDescriptor<
    [],
    {
        child_items: number;
        progress_child: Enum<
            { Complete: undefined; LastKey: Binary; ToStart: undefined },
        >;
        progress_top: Enum<
            { Complete: undefined; LastKey: Binary; ToStart: undefined },
        >;
        size: number;
        top_items: number;
    },
    false,
    never,
>

Migration progress.

This stores the snapshot of the last migrated keys. It can be set into motion and move forward by any of the means provided by this pallet.