Host the cooking walk-through as a test suite

The cooking_walk integration test moves here from the separate
cooking_walk_test mod as test_suites/cooking_walk, mounted as the virtual
mod cooking__cooking_walk only with --itest=cooking_walk.

manifest.json

@@ -33,5 +33,8 @@
       "show_on_start": true,
       "priority": 20
     }
+  ],
+  "test_suites": [
+    {"id": "cooking_walk", "activate": ["--itest=cooking_walk"]}
   ]
-}
+}