feat: remove "extras" packages from factory

[mauromorales]

When a user with BYOI passes their base image through the factory, we should only install packages required by kairos to function. No "extras" should be added like nano, vim, or anything else that the user did not request.

IMO we should split images/Dockerfile.ubuntu into something like images/Dockerfile.ubuntu-factory and images/Dockerfile.ubuntu-base (or a better name) where the former only contains packages that are required to convert any image into a Kairos distro, while the latter will be used as --BASE_IMAGE=ubuntu-base.