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/redis/module.json

@@ -47,6 +47,22 @@
       "why": "modules on any machine that were granted a cache"
     }
   ],
+  "data": {
+    "own": [
+      {
+        "id": "data",
+        "path": "${dir:data}",
+        "class": "cache",
+        "why": "the cache's own snapshot"
+      }
+    ],
+    "consumers": {
+      "redis-cache": {
+        "class": "cache",
+        "why": "a cache: nothing in this mesh requires it, and a consumer that kept data in it would be using a cache as a store"
+      }
+    }
+  },
   "resources": [
     {
       "id": "state",