Add the ability to download the images instead of building on make-[0|1]

[knabben]

There were some discussion and later accordance on how to get LATEST version of binaries on linux and windows with a faster approach than building everything from zero

from @jsturtevant comments on how CAPZ does the process for the CI:

* somehting like VERSION=v1.23.1 make and you get all the things 1.23.1
* then that could be used to curl the CI versions so you don't have to build everything from source if you want to just try something out
* curl "https://storage.googleapis.com/k8s-release-dev/ci/$$CI_VERSION/bin/windows/amd64"
* where you can get the latest ci version from https://storage.googleapis.com/kubernetes-release-dev/ci/latest.txt
* there is a short url you can use for each version https://dl.k8s.io/ci/latest-{version}.txt"
*
if [[ "${KUBERNETES_BRANCH:-}" =~ "release-" ]]; then
            CI_VERSION_URL="https://dl.k8s.io/ci/latest-${KUBERNETES_BRANCH/release-}.txt"
        else
            CI_VERSION_URL="https://dl.k8s.io/ci/latest.txt"
        fi

* https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/ed345c6b0552c53f2cb02f9c3bf5eb6f2e0cb64d/scripts/ci-entrypoint.sh#L76-L80

The control of build vs. download must be set on variables.yaml with a boolean build_from_source.

[knabben]

/assign