fix(ui): disable width and height output on image batch output

There's a technical challenge with outputting these values directly. `ImageField` does not store them, so the batch's `ImageField` collection does not have width and height for each image.

In order to set up the batch and pass along width and height for each image, we'd need to make a network request for each image when the user clicks Invoke. It would often be cached, but this will eventually create a scaling issue and poor user experience.

As a very simple workaround, users can output the batch image output into an `Image Primitive` node to access the width and height.

This change is implemented by adding some simple special handling when parsing the output fields for the `image_batch` node.

I'll keep this situation in mind when extending the batching system to other field types.

invokeai/frontend/web/src/features/nodes/util/schema/parseSchema.ts

@@ -58,6 +58,9 @@ const isAllowedOutputField = (nodeType: string, fieldName: string) => {
   if (RESERVED_OUTPUT_FIELD_NAMES.includes(fieldName)) {
     return false;
   }
+  if (nodeType === 'image_batch' && fieldName !== 'image') {
+    return false;
+  }
   return true;
 };