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/keycloak/module.json

@@ -71,6 +71,15 @@
   "own-secrets": {
     "admin": "${dir:state}/admin.secret"
   },
+  "data": {
+    "consumers": {
+      "oidc-client": {
+        "class": "rebuildable",
+        "in": "postgres-database",
+        "why": "a consumer's client is made again from its declaration, with a new secret"
+      }
+    }
+  },
   "resources": [
     {
       "id": "mesh-state",