Include attachment details in the article's detailed response

[injoonH]

GET /articles/<id>/

Before

{
  "attachments": [
    [1],
    [2],
    [3]
  ]
}

After

{
  "attachments": [
      {
      "id": 1,
      "created_at": "2023-06-17T18:08:22.264122+09:00",
      "updated_at": "2023-06-17T18:08:22.264122+09:00",
      "deleted_at": "0001-01-01T08:27:52+08:27:52",
      "file": "...",
      "size": 1234,
      "mimetype": "image/png"
    }
  ]
}

[injoonH]

Fixed frontend code in the commit: sparcs-kaist/new-ara-web@bb25417. (Forgot to make a PR...)