Declare every module's data; the backup holder measures it (hq ADR 0233)

Backup lines are derived from each module's data section instead of written by hand; the holder
measures declared items, reads the array under them, and deletes a retired item only after a last
restore point; the Go providers say each held consumer's size so an empty replacement is seen.

modules/n8n/module.json

@@ -39,6 +39,22 @@
       "why": "the n8n editor, its REST API and the webhook endpoints workflows are triggered through; a public name is the route's"
     }
   ],
+  "data": {
+    "own": [
+      {
+        "id": "data",
+        "path": "${dir:data}",
+        "class": "valuable",
+        "why": "the instance's encryption key, settings and binary data; workflows are in the database"
+      },
+      {
+        "id": "cache",
+        "path": "${dir:cache}",
+        "class": "cache",
+        "why": "scratch space"
+      }
+    ]
+  },
   "resources": [
     {
       "id": "state",