feat(infra): OCI NLB 전용 Ingress 및 Terraform 관리 편입 - #19

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, imranismail/setup-kustomize@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/