dm-verity

We need to verify initoverlayfs on boot, to check it's contents are correct, we must ensure whatever we use can work on a erofs file within a vfat, ext4, erofs boot partition.

dm-verity probably makes more sense to use the verity within the initoverlayfs, because if initoverlayfs is a file, the directory it's on may not have verity (for example if it's an initoverlayfs file on ESP vfat).