Fix Shopper Insights PayPal flow and PayPal Vault flow

[tdchow]

Summary of changes

• Add missing path to Shopper Insights App Link URL
• Add required postal code for the demo app vault request.

Vault error:

{
   "error": {
      "debugId": "b891a597f94c4",
      "errorDetails": [
         {
            "description": "The specified country requires a postal code.",
            "issue": "SHIPPING_POSTAL_CODE_REQUIRED"
         }
      ],
      "errorMessage": "The requested action could not be performed, semantically incorrect, or failed business validation. --- :",
      "errorName": "UNPROCESSABLE_ENTITY",
      "paypalHttpStatus": 422
   }
}

Checklist

• Added a changelog entry
• Relevant test coverage
• Tested and confirmed payment flows affected by this change are functioning as expected

Authors

List GitHub usernames for everyone who contributed to this pull request.