Creates a retrospective process group

curl --request POST \
  --url https://api.rootly.com/v1/retrospective_processes/{retrospective_process_id}/groups \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '
{
  "data": {
    "type": "retrospective_process_groups",
    "attributes": {
      "sub_status_id": "<string>",
      "position": 123
    }
  }
}
'

{
  "data": {
    "id": "1d806a63-a226-43cc-8f64-c5217f2d58cb",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "4efccb2d-0e97-4943-900c-f862a9c45b71",
      "sub_status_id": "390d4094-6ad5-4017-82b3-ca6f4ec3ac2c",
      "position": 3,
      "updated_at": "2026-01-19T14:17:31.663-08:00",
      "created_at": "2026-01-19T14:17:31.663-08:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}