Retrieves an incident retrospective

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

{
  "data": {
    "id": "99ac00b5-4c7b-4fc1-a778-4ac90f93da25",
    "type": "incident_post_mortems",
    "attributes": {
      "incident_id": "2cb9ae3a-f2ef-4fff-83a9-67e56ac9ff9b",
      "title": "Rerum aut omnis totam.",
      "status": "draft",
      "url": "https://test.rootly.com/account/post_mortems/rerum-aut-omnis-totam",
      "short_url": null,
      "content": null,
      "published_at": null,
      "started_at": "2025-09-16T17:15:02.209-07:00",
      "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": "2025-09-16T17:15:03.176-07:00",
      "updated_at": "2025-09-16T17:15:03.191-07:00"
    },
    "relationships": {
      "incident_retrospective_steps": {
        "data": [
          {
            "id": "bd189e7b-5848-408f-9f60-f3e7c8b22471",
            "type": "incident_retrospective_steps"
          }
        ]
      }
    }
  }
}