Retrieves an incident retrospective

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

{
  "data": {
    "id": "7c95579f-0e28-46d1-b6c6-7bbe47a2152f",
    "type": "incident_post_mortems",
    "attributes": {
      "incident_id": "1b0ae8b0-f3ae-48bc-bd41-52cee35c31e8",
      "title": "Nulla nihil atque in.",
      "status": "draft",
      "url": "https://test.rootly.com/account/post_mortems/nulla-nihil-atque-in",
      "short_url": null,
      "content": null,
      "published_at": null,
      "started_at": "2026-01-19T01:06:11.768-08:00",
      "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": "2026-01-19T01:06:12.135-08:00",
      "updated_at": "2026-01-19T01:06:12.139-08:00"
    },
    "relationships": {
      "incident_retrospective_steps": {
        "data": [
          {
            "id": "5435c736-dd4b-4273-920f-e020516e8264",
            "type": "incident_retrospective_steps"
          }
        ]
      }
    }
  }
}