Add Helm chart for the expense tracker (app, Postgres, ingress, backups)

- Deployment/Service for the app, StatefulSet/Service for Postgres 17
- Secrets (DB password, session secret, Google client, allowed e-mails) via
  ExternalSecret from OpenBao
- Ingress with a Let's Encrypt certificate, NetworkPolicy for Postgres
- Nightly pg_dump CronJob
- Optional OpenBao OIDC provider setup script

Co-Authored-By: Claude Sonnet 5 <[email protected]>

Chart.yaml

@@ -0,0 +1,16 @@
+apiVersion: v2
+name: expense-tracker
+description: Helm chart to run the Budget / expense tracker (web app + Postgres) on Kubernetes
+type: application
+version: 0.1.0
+appVersion: "b6da854"
+home: https://git.smokyzone.de/SmokyZone/expense_tracker-gitops
+sources:
+  - https://git.smokyzone.de/SmokyZone/expense_tracker-gitops
+  - https://git.smokyzone.de/SmokyZone/budget
+keywords:
+  - budget
+  - expense-tracker
+  - postgres
+maintainers:
+  - name: SmokyZone