Migrate Infra code to separate repo called k/infrastructure

[upodroid]

The code in the infra folder should be moved to a new repository called kubernetes/infrastructure

You can have a look at https://github.com/borg-land/k8s.io/tree/new-infra-repo for what I think the repo will look like. We want to store only terraform code for our infrastructure and Kubernetes manifests in that repo.

I'm going to use that repo for terraform automation and unify all the kubernetes manifests for all our clusters to a central location.

/cc @xmudrii @ameukam @BenTheElder @dims

[xmudrii]

I'm +1 for this change, we also had a chance to discuss it at KubeCon and I think it would help to implement better CI/CD workflows with Prow and Argo. However, I'd like to experiment a bit more with the repo structure, I'll try to do it in the next day or two and get back with results.

[BenTheElder]

I'm kind of -1 on this change, we have a lot of overlap between terraform and non-terraform (e.g. the bash, the IAM auditing, etc), I'd like to see the terraform automation we adopt be safer instead.

Also, anytime we move code to a new repo there's a lot of broken inbound links and general churn, so in most cases we've broken things out to make them easier to consume (e.g. using kind or prow the project without other random test-infra hackery), whereas this whole repo is soley infra configs for kubernetes.