Make it possible to run squashing without accessing Docker daemon

[goldmann]

It should be possible to run squashing on a provided tar archive containing the image.

[goldmann]

Implementing this shouldn't be that hard. What we will need to check is for sure that the exported archive does contain single image/tag. If we would have more than one - we would not be able to select which one the user was thinking about.

From top of my head - I'm also unsure if untagged images contain repositories or manifest.json files to describe the image. If these files do not exist in exported archive, then we would either: fail or read all layers to determine the top (image) layer.

[qwertycody]

Any update on if you guys might try to target doing this?

[gabs79]

In addition to squash off a provided tar, I would also be helpful to do it off a container image registry.

[cmahnke]

This would als be useful when using cloud based builders like kaniko...