Add spec-compliant config.json files

xnnpack/config.json

@@ -0,0 +1,18 @@
+{
+  "$schema": "https://huggingface.co/software-mansion/react-native-executorch-spec/resolve/main/config.schema.json",
+  "model": "craft",
+  "family": "craft",
+  "capabilities": [
+    "text-detection"
+  ],
+  "backend": "xnnpack",
+  "license": "mit",
+  "variants": [
+    {
+      "file": "craft_xnnpack_int8.pte",
+      "precision": "int8",
+      "quantized": true,
+      "default": true
+    }
+  ]
+}