docs: change field name from id to $id in schema.json file (#42528)

fix error "SchematicsMyService" schema is using the keyword "id" which its support is deprecated. Use "$id" for schema ID.

PR Close #42528

aio/content/examples/schematics-for-libraries/projects/my-lib/schematics/my-service/schema.json

@@ -1,6 +1,6 @@
 {
   "$schema": "http://json-schema.org/schema",
-  "id": "SchematicsMyService",
+  "$id": "SchematicsMyService",
   "title": "My Service Schema",
   "type": "object",
   "properties": {
@@ -25,4 +25,4 @@
   "required": [
     "name"
   ]
-}
+}