arrstack: mount legacy mediafs CephFS via static PV/PVC

Exposes the legacy mediafs filesystem to the arrstack namespace for the
upcoming mediamover tool. Adds a ceph-mediafs-secret VaultStaticSecret in
csi-cephfs and a 10Ti static RWX PV/PVC pair bound by claimRef.

apps/base/arrstack/kustomization.yaml

@@ -7,8 +7,10 @@ resources:
   - vaultauth.yaml
   - pv-media-tv.yaml
   - pv-media-movies.yaml
+  - pv-mediafs.yaml
   - pvc-media-tv.yaml
   - pvc-media-movies.yaml
+  - pvc-mediafs.yaml
   - media-bucket.yaml
   - backups-bucket.yaml
   - postgres