Get EndUser named dates

curl --request GET \
  --url https://app.herondata.io/api/end_users/{end_user_id_or_heron_id}/named_dates \
  --header 'x-api-key: <api-key>'

{
  "named_dates": [
    {
      "date": "2025-06-19",
      "name": "last_transaction"
    }
  ]
}