Add TagManager APIs for Root Product Id

Summary:
* Implement getter and setter for new field root_product_id from contextprop baggage in TagManager
* As part of setter, log override event in ```TagManagerTracingEventLogger```

Differential Revision: D70340893

fbshipit-source-id: 139396c950d69739fc5ec24d6af0920bb4fe3432

third-party/thrift/src/thrift/lib/hack/src/ThriftContextPropState.php

@@ -565,8 +565,15 @@ public function clearBaggageFlags1ByName(
   }
 
   // Getters for the root_product_id
-  public function getRootProductId()[leak_safe]: ?int {
-    return $this->storage->baggage?->root_product_id;
+  public readonly function getRootProductId()[leak_safe]: ?int {
+    if ($this->storage->baggage is null) {
+      return null;
+    }
+    $root_product_id = $this->storage->baggage?->root_product_id;
+    if ($root_product_id is null) {
+      return null;
+    }
+    return ($root_product_id as int);
   }
 
   // Immutable setter for the root_product_id