Review array merge semantics

[blaggacao]

Associative array merges should by default behave like they are intended to behave by upstream kustomize.

We can gather research material for nickel here, as well.

See also:

• https://github.com/kubernetes-sigs/kustomize/blob/f61b075d3bd670b7bcd5d58ce13e88a6f25977f2/cmd/config/docs/api-conventions/merge3.md#associative-keys
• https://github.com/kubernetes-sigs/kustomize/blob/f61b075d3bd670b7bcd5d58ce13e88a6f25977f2/cmd/config/docs/api-conventions/merge2.md
• and further k8s material