Better default filters for metafield and metaobject definitions

When exporting metafield and metaobject definitions, we now automatically exclude Shopify-managed definitions that cannot be imported due to API restrictions.

🔧 Improvements

• Metafield definition exports – automatically exclude Shopify namespace definitions that cannot be imported.
• Metaobject definition exports – filter out Shopify-managed definitions by default to prevent import failures.
• Pre-configured filters – smart defaults are applied when selecting these object types, but can be customized as needed.