FEAT(postgresql): configure vault

- to use externalsecret for postgresq...
- Add ExternalSecret to pull vault config from Vault itself
- Add RBAC for vault token reviewer (kubernetes auth)
- Update helm-values to mount secret as config
- Connection string is now stored in Vault, not in git

vault/kustomization.yaml

@@ -2,3 +2,5 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
 - cluster-secret-store.yaml
+- external-secret.yaml
+- rbac.yaml