Create an idea subscription

{
  "idea_subscription": {
    "email": "username@example.com"
  }
}

{
  "idea_subscription": {
    "id": "6776881149499782711",
    "idea_id": "58056975",
    "created_at": "2019-01-01T00:00:00.000Z",
    "portal_user": {
      "id": "6776881149490241023",
      "name": "username@example.com",
      "email": "username@example.com",
      "created_at": "2019-01-01T00:00:00.000Z"
    },
    "idea": {
      "id": "58056975",
      "name": "Idea 1",
      "reference_num": "PRJ1-I-1",
      "created_at": "2019-01-01T00:00:00.000Z",
      "updated_at": "2019-01-01T00:00:00.000Z",
      "workflow_status": {
        "id": "3259216",
        "name": "New",
        "position": 1,
        "complete": false,
        "color": "#dce7c6",
        "workflow_status_category": null
      },
      "description": {
        "id": "103757394",
        "body": "Description of idea 1",
        "notable_id": "58056975",
        "notable_type": "Ideas::Idea",
        "editor_version": 1,
        "created_at": "2019-01-01T00:00:00.000Z",
        "updated_at": "2019-01-01T00:00:00.000Z",
        "attachments": []
      },
      "url": "https://company.aha.io/ideas/ideas/PRJ1-I-1",
      "resource": "https://company.aha.io/api/v1/ideas/PRJ1-I-1"
    }
  }
}