CreateSoci creates a SOCI index(`rawRef`).

PushSoci pushes a SOCI index(`rawRef`) `hostsDirs` are used to resolve image `rawRef`.

SociAppendDefaultLabelsHandlerWrapper makes a handler which appends image's basic information to each layer descriptor as annotations during unpack.

TargetSizeLabel is a label which contains layer size.

TargetSociIndexDigestLabel is a label which contains the digest of the soci index.