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": "caa8f97e-b0df-47a9-b3ce-819ebd4c0311",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "346b8aa2-36a9-488c-9b19-ffff1590d183",
      "sub_status_id": "2a7f05ed-264a-4068-a092-2a1320e7b92f",
      "position": 3,
      "updated_at": "2026-02-18T14:04:37.955-08:00",
      "created_at": "2026-02-18T14:04:37.955-08:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}