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/icecast/module.json

@@ -37,6 +37,16 @@
       "why": "streams in from sources (HTTP PUT) and out to listeners, plus the status and admin pages; a public name is its route"
     }
   ],
+  "data": {
+    "own": [
+      {
+        "id": "logs",
+        "path": "${dir:logs}",
+        "class": "cache",
+        "why": "the streaming server's logs"
+      }
+    ]
+  },
   "resources": [
     {
       "id": "mesh-state",