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": "27872418-a369-455d-a467-1b0a327137b1",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "636b0195-3d15-4ff4-8f45-56246328262e",
      "sub_status_id": "06be5c6d-b846-4437-ae6a-b68319b7ef44",
      "position": 3,
      "updated_at": "2025-11-06T13:28:55.670-08:00",
      "created_at": "2025-11-06T13:28:55.670-08:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}