add kustomize support

[rochacon]

By adding the kustomization.yaml we allow this repository be to easily patched via kustomize (also embedded on kubectl) to adjust settings for different environments.

Extending via kustomization.yaml

A consumer project can reference this repository like this:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  # for testing this PR, use: github.com/kumbuca/n8n-kubernetes-hosting
  - github.com/n8n-io/n8n-kubernetes-hosting?ref=main

This can be applied with kubectl apply -k .

Rendering directly with kubectl:

kubectl kustomize "github.com/n8n-io/n8n-kubernetes-hosting"
kubectl apply -k "github.com/n8n-io/n8n-kubernetes-hosting?ref=main"