Create a kairos "installer"

[jimmykarily]

Right now, the way to create a Kairos "derivative" image is to either feed a base image to our dockerfiles of take one of our images and use it as a base image for another dockerfile.

Our dockerfiles are rather complex and the logic very hard to follow. This makes them very difficult to extend and test.
Also, using dockerfiles, makes docker a hard dependency (or some other tool that can build dockerfiles anyway).

We could move all the dockerfile logic in a go binary (let's call it the "installer" for now but we need a better name to avoid confusion with the agent that installs Kairos on the machines). By doing that, one would simply run the binary inside an OS and all the dependencies to make it a Kairos OS would be installed with no additional dependencies.