List end users

curl --request GET \
  --url https://app.usechar.ai/api/end-users \
  --header 'Authorization: Bearer <token>'

{
  "users": [
    {
      "id": "<string>",
      "organization_id": "<string>",
      "external_id": "<string>",
      "email": "<string>",
      "metadata": "<string>",
      "last_activity_at": "2023-11-07T05:31:56Z",
      "created_at": "2023-11-07T05:31:56Z",
      "updated_at": "2023-11-07T05:31:56Z"
    }
  ],
  "total": 123
}