Retrieves an incident retrospective

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

{
  "data": {
    "id": "d66889fe-a747-4855-8843-fbf1abe7fe8a",
    "type": "incident_post_mortems",
    "attributes": {
      "incident_id": "56287e52-6996-45c6-8c7f-1e6f2a0c453f",
      "title": "Id et eveniet fugiat.",
      "status": "draft",
      "url": "https://test.rootly.com/account/post_mortems/id-et-eveniet-fugiat",
      "short_url": null,
      "content": null,
      "published_at": null,
      "started_at": "2025-07-10T10:26:42.658-07:00",
      "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": "2025-07-10T10:26:43.593-07:00",
      "updated_at": "2025-07-10T10:26:43.602-07:00"
    },
    "relationships": {
      "incident_retrospective_steps": {
        "data": [
          {
            "id": "9713d703-f347-4a5e-965d-fb5f11e05bfb",
            "type": "incident_retrospective_steps"
          }
        ]
      }
    }
  }
}