[Isulad] Feature Request: Smart loading for remote images

Hi iSulad owners, Startgz[1] is an index-able format for tar.gz file, which is introduced by Brad Fitzpatrick[2]. It has the great feature on remote items for pulling-smartly-when-needed. With it, the container creating time could be greatly reduced. It is already supported by containerd [3]. I've digged some on it, let's discuss it on this week's meeting and see what we can do. [1]: crfs: https://github.com/google/crfs [2]: https://github.com/bradfitz [3]: containerd/stargz-snapshotter: https://github.com/containerd/stargz-snapshotter Best Regards, Lu Jingxiao