Retrieves an incident retrospective

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

{
  "data": {
    "id": "83cc15d5-8caf-4f79-8b5a-e286f4c1a44c",
    "type": "incident_post_mortems",
    "attributes": {
      "incident_id": "7df58038-f361-4d46-90cf-74ea9900e7bd",
      "title": "Pariatur ex repellat nemo.",
      "status": "draft",
      "url": "https://test.rootly.com/account/post_mortems/pariatur-ex-repellat-nemo",
      "short_url": null,
      "content": null,
      "published_at": null,
      "started_at": "2026-02-02T00:07:46.867-08:00",
      "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": "2026-02-02T00:07:47.344-08:00",
      "updated_at": "2026-02-02T00:07:47.350-08:00"
    },
    "relationships": {
      "incident_retrospective_steps": {
        "data": [
          {
            "id": "a245ddc0-da99-449a-859c-97bf3dcd9c6e",
            "type": "incident_retrospective_steps"
          }
        ]
      }
    }
  }
}