[codex] Add etcd snapshot store manifests

[boxp]

Summary

• Add a new Argo CD application for etcd-snapshot-store.
• Manage namespace etcd-snapshots, PVC etcd-snapshots, and a single-replica Deployment in lolice manifests.
• Use Longhorn ReadWriteOnce storage with a 10Gi request.
• Label the storage pod with app.kubernetes.io/name=etcd-snapshot-store so the arch upgrade workflow can discover it by selector.
• Add the plan at docs/project_docs/BOXP-2-etcd-snapshot-store-manifest/plan.md.

Validation

• git diff --check
• kubectl kustomize argoproj/etcd-snapshot-store via bitnami/kubectl:latest
• kubectl kustomize argoproj via bitnami/kubectl:latest
• codex review --uncommitted

Related

• Companion arch PR: [codex] Store etcd snapshots in Longhorn PVC arch#9522

[github-actions]

ArgoCD Diff Result

Auth path: tailscale

アプリケーション: etcd-snapshot-store の差分

パス: argoproj/etcd-snapshot-store