ConfigMaps items are generated with random order

# Description

`kustomize build .` produces configmap items in a random order and although it is somehow benign since it produces equivalent YAML files, it would be great if the build outputs are consistent and reproducible.

I tested it with kustomize v4.4.1

Start by reproducing the ordering difference with `kustomize build .` using the ConfigMap case described in the issue, then trace the ConfigMap generation path in the Go code. Done means repeated builds produce the same ConfigMap item order and equivalent existing output remains unchanged.

Written by the indexing model from the issue text.