Unpack local image

[Ludea]

Is your feature request related to a problem? Please describe.

I use cos toolkit to build a derivative. When using arm builder, instead of unpack the built img, it pull and unpack downloaded img

Describe the solution you'd like

I would like to unpack a local image

Describe alternatives you've considered

Additional context

https://github.com/mudler/luet/blob/bb88fe7e9cbdce2a59edc8068c27bb4603ded5f0/pkg/helpers/docker/docker.go#L130 maybe split this func into 2 func and add an option to luet util unpackto specify local image name

[mudler]

good point, definetly luet util unpack can take an optional --local flag