Add support for dockershim pod annotations

[miaoyq]

Dockershim use container labels to identify whether a docker container is a sandbox or a regular container. I have sent a PR https://github.com/moby/moby/pull/36181 in moby project to pass the label to the annotations of OCI runtime spec.

This commit add support for dockershim pod annotations.

/cc @sameo

Signed-off-by: Yanqiang Miao miao.yanqiang@zte.com.cn

[sameo]

@miaoyq Mostly looks good to me, except for the missing comments on the exported data.

[miaoyq]

@sameo Thanks, will add the comments. :-)

[sameo]

LGTM