hack/flux-install.sh does not work with modern docker credsStore settings

Kubectl currently does not support Docker credential helpers:

• https://kubernetes.io/docs/concepts/containers/images/#configuring-nodes-to-authenticate-to-a-private-registry

Modern versions of Docker on MacOS do not (easily or sanely) allow the end user to disable non base64 credential helpers settings:

• https://github.com/docker/for-mac/issues/4100
• https://github.com/docker/for-mac/issues/1826

We should either update the documentation to reflect a much easier way of installing flux (IE - creating the registry credentials manually), or implement this in the hack/flux-install.sh script. In my opinion, we should not force users to roll back their credential helpers to an older (and possibly unsupported in the future) method of storing credentials (IE - base64).

Example documentation for a manual flux install, where BigBang manages the customized flux.yaml script for Flux pointing at IronBank (through scripts/deploy/flux.yaml):

kubectl create ns flux-system
kubectl create secret docker-registry private-registry --docker-server=registry1.dso.mil --docker-username=<username> --docker-password=<password> --docker-email=<email> -n flux-system
kubectl apply -f scripts/deploy/flux.yaml
flux check
kubectl delete secret private-registry -n flux-system

The above commands are what I use, and are verified to be working.

Or - We could just make it another helm chart