add minikube bootcamp image to registry

[ComradeProgrammer]

Following https://github.com/kubernetes/test-infra/blob/master/config/jobs/image-pushing/README.md
Changes are also being made simultaneously on minikube side kubernetes/minikube#21904
(There will be a file called hack/prow/image/kubernetes-bootcamp/cloudbuild.yaml in minikube)

[k8s-ci-robot]

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[ComradeProgrammer]

We are trying to migrate some simple image to k8s registry, so we just chose the easiest one. If this works, we will migrate more of them.