sealer support to load offline image at build stage

[kakaZhou719]

Issue Description

In some case user has some offline images that can be loaded to the cluster image at build stage.

Type: feature request

Describe what feature you want

sealer build -t my-image:v1 -f Kubefile --load-image-files /path/nginx.tar

will load "nginx.tar " to cluster image.

Additional context

Add any other context or screenshots about the feature request here.

[kakaZhou719]

sealer build -t my-image:v1 -f Kubefile --load-local-images nginx:v1, mysql:latest

will load local images( already existed on the local disk: docker data dir) to cluster image.

[jsparter]

/assign