Retrieves an incident retrospective

curl --request GET \
  --url https://api.rootly.com/v1/post_mortems/{id} \
  --header 'Authorization: Bearer <token>'

{
  "data": {
    "id": "401f1b27-67d1-471a-b49c-736217f432d1",
    "type": "incident_post_mortems",
    "attributes": {
      "incident_id": "f6f87090-1208-4a7e-b0e2-4ea56a4bdaba",
      "title": "Id aspernatur blanditiis tempora.",
      "status": "draft",
      "url": "https://test.rootly.com/account/post_mortems/id-aspernatur-blanditiis-tempora",
      "short_url": null,
      "content": null,
      "published_at": null,
      "started_at": "2025-12-19T10:18:51.101-08:00",
      "mitigated_at": null,
      "resolved_at": null,
      "cancelled_at": null,
      "show_timeline": true,
      "show_timeline_starred_only": false,
      "show_timeline_genius": true,
      "show_timeline_trail": true,
      "show_timeline_tasks": true,
      "show_timeline_action_items": true,
      "show_timeline_order": "desc",
      "show_functionalities_impacted": true,
      "show_services_impacted": true,
      "show_groups_impacted": true,
      "show_action_items": true,
      "created_at": "2025-12-19T10:18:51.575-08:00",
      "updated_at": "2025-12-19T10:18:51.580-08:00"
    },
    "relationships": {
      "incident_retrospective_steps": {
        "data": [
          {
            "id": "a328f7fe-9908-4b42-8171-b459104003f1",
            "type": "incident_retrospective_steps"
          }
        ]
      }
    }
  }
}