Updated MetafieldsSetInput.type to be nullable for metafieldsSet mutation

As part of the 2023-01 GraphQL Admin API release, we've updated the metafieldsSet API to make the MetafieldsSetInput.type field nullable. When the metafield you are trying to mutate already has corresponding metafield definitions, you can simplify the mutation by omitting the type field from its arguments. The type field is still required when the metafield doesn't have a corresponding definition to the given ownerId, namespace and key.

For more information, refer to the metafieldsSet mutation.