REFACTOR(repo): move vault/ to manifests/

- Move ExternalSecret files from vault/ to manifests/secret.yaml
- Merge multiple secrets with --- separator (immich)
- Update kustomization.yaml references
- Remove vault/ folders

Apps: umami, immich, code-server

code-server/kustomization.yaml

@@ -2,5 +2,5 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 namespace: code-server
 resources:
-- vault/code-server-password.yaml
+- manifests/secret.yaml
 - manifests/rbac.yaml