Make nydus image more compatible with OCI #463
Description
A personal idea by @hsiangkao, but I agree with the point.
- Allow ctr/crictl/nerdctl pull directly without nydus snapshotter;
- Use
zstd:chunked/estargzcompression algorithm for blob layer; - Allow lzay pull for each blob layer with nydus snapshotter;
- The bootstrap layer (as final layer) is compatible with erofs format (erofs on fscache), and wrap with tar (allow pulling without nydus snapshotter);