org.osbuild.containers.storage.conf: Add transient_store option

This is used by the automotive project, but is also useful for edge.

stages/org.osbuild.containers.storage.conf

@@ -46,6 +46,10 @@ SCHEMA = r"""
         "description": "container storage run directory.",
         "type": "string"
       },
+      "transient_store": {
+        "description": "Make the container store not persist across reboot.",
+        "type": "boolean"
+      },
       "options": {
          "$ref": "#/definitions/storage-options"
       }