Adding loading state for `build_image`

[bolasim]

Is your feature request related to a problem? Please describe. When dealing with large weight files (this is about ~5Gb) it looks like truss hangs when its calculating hashes and making the build context. It would be great if we have a spinner and some kind of communication about what is happening while this being calculated here.

Describe the solution you'd like We could add a spinner that says Preparing docker context or something to that effect while doing this so it doesn't look like it hangs.