Add command that builds a KDT-expected docker image

[pratikmallya]

The publish command expects a locally built image with a certain tag. It expects an image with tag local-registry/<IMAGE_NAME> to exist and simply tags the local-registry/<IMAGE_NAME>:latest with a git hash and pushes it.

This is not ideal as:

• this is an implicit assumption on how docker images should be built. local-registry is not a well known standard.
• its possible that the :latest tag may be misleading. e.g. the image could have been built on a different version of the repo. Tagging the repo with the hash implies that it was built specifically for that hash, which publish doesn't really know if its true.

Proposed solution:

• a kdt build command that builds a docker image in the style that KDT expects
• not really sure if the kdt push behavior can be changed as its already in use. Perhaps it shouldn't re-tag latest but simply check if an image with the expected tag exists and push them. Could be enabled in a --strict mode I guess.

[joshk0]

What do you think about just erasing the prefix?

In other words kdt push foo retags the foo image as gcr.io/your-prefix/foo:sha1.

Most of the reasons that drive the local-registry thing had to do with people running local stacks on Docker for Mac, which is not a concern for the vast majority of KDT users at this point.