In containerd, there is a size limit for label size (4096 chars). Currently if an image has many layers (> (4096-39)/72 > 56), `containerd.io/snapshot/cri.image-layers` will hit the limit of label size and the unpack will fail. This commit fixes this by limiting the size of the annotation. Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>