feat(storage): migrate SeaweedFS S3 credentials to VSO; mount s3.json from Secret

Previously s3.json was embedded in the seaweedfs-filer-config ConfigMap
with hardcoded minioadmin credentials, and the config volume was mounted
at /etc/seaweedfs/ (overwriting filer.toml with its own directory mount).

- Remove s3.json from ConfigMap; fix the config volume to mount only
  filer.toml via subPath so both files coexist under /etc/seaweedfs/.
- Add vault-secrets.yaml with VaultStaticSecrets that VSO syncs from
  OpenBao secret/seaweedfs: seaweedfs-s3-credentials (S3_ACCESS_KEY /
  S3_SECRET_KEY) and seaweedfs-s3-json (s3.json as a JSON template).
- Mount seaweedfs-s3-json Secret at /etc/seaweedfs/s3.json via subPath.

base/storage/seaweedfs-config.yaml

@@ -16,22 +16,6 @@ data:
     enabled        = true
     port           = 8333
 
-  s3.json: |
-    {
-      "identities": [
-        {
-          "name": "minioadmin",
-          "credentials": [
-            {
-              "accessKey": "minioadmin",
-              "secretKey": "minioadmin"
-            }
-          ],
-          "actions": ["Admin", "Read", "Write", "List", "Tagging"]
-        }
-      ]
-    }
-
   master.toml: |
     [master.maintenance]
     sleep_minutes          = 17