List packs for the shop

{  "items": [    {      "id": "497f6eca-6276-4993-bfeb-53cbbbba6f08",      "shop_id": "string",      "name": "string",      "mode": "fixed",      "base_product_id": "string",      "base_variant_id": "string",      "eligible_product_ids": [        "string"      ],      "eligible": [        {          "product_id": "string",          "variant_id": "string",          "title": "string",          "image_url": "string",          "price_each": "string"        }      ],      "tiers": [        {          "size": 1,          "pack_price": 1,          "shopify_product_id": "string",          "shopify_variant_id": "string",          "shopify_handle": "string"        }      ],      "status": "draft",      "created_at": "2019-08-24T14:15:22Z",      "updated_at": "2019-08-24T14:15:22Z"    }  ]}