Update Product

Noted:

• Variant's image should be one of related Product's image
• while update options, variants object are needed, and every single variant.option should match with options object.
• while all variant's image is empty, need_variant_image will automatically update to false
• while variant's image is present, need_variant_image flag will update to true automatically.
• while update variant's image, either using image object, or image_id is fine, but if both present, image_id will be used.
• while update/create metafield, system wouldn't delete metafield record existing.