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": "c1a5ca3b-6dfd-4189-aa19-dda7b6ba4350",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "9e9ade3b-c147-47ff-91ba-a6f5eb1014f6",
      "sub_status_id": "beb82c5e-32c8-40c2-adda-b1e4d74957ad",
      "position": 3,
      "updated_at": "2025-10-20T08:33:46.321-07:00",
      "created_at": "2025-10-20T08:33:46.321-07:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}