[tf.data service] Update standalone iterator name from "iterator" to "Iterator".

This makes it consistent with regular tf.data iterators, so xprof tooling can treat them the same.

PiperOrigin-RevId: 342766295
Change-Id: Ied1de2d801df3668606dc187da0ad48c52927350

tensorflow/core/data/standalone.cc

@@ -124,7 +124,7 @@ Status Dataset::MakeIterator(std::unique_ptr<SplitProvider> split_provider,
   // Create the iterator from the dataset.
   std::unique_ptr<IteratorBase> iterator;
   TF_RETURN_IF_ERROR(dataset_->MakeIterator(ctx.get(), /*parent=*/nullptr,
-                                            "iterator", &iterator));
+                                            "Iterator", &iterator));
 
   *result = WrapUnique(new Iterator(iterator.release(), ctx.release()));