kustomize secret generator plugin を実装する
https://github.com/kubernetes-sigs/kustomize/blob/master/examples/secretGeneratorPlugin.md
https://github.com/kubernetes-sigs/kustomize/tree/master/docs/plugins
https://github.com/monopole/sopsencodedsecrets
https://github.com/kubernetes-sigs/kustomize/tree/kustomize/v3.5.3/plugin/someteam.example.com/v1
https://github.com/kubernetes-sigs/kustomize/issues/1641
CGO_ENABLED=1 でビルドした kustomize じゃないとダメそうに思える
https://github.com/golang/go/issues/19569