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": "d492a783-e877-458d-89c0-090f0012044c",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "5c412969-3b43-4605-b867-7ac4d94c1723",
      "sub_status_id": "6a695710-9878-4fba-8170-501abe59307b",
      "position": 3,
      "updated_at": "2026-02-07T16:50:15.164-08:00",
      "created_at": "2026-02-07T16:50:15.164-08:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}