Creates a retrospective process group step

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

{
  "data": {
    "id": "3ff5fce6-e810-4599-a24e-fba87225c27b",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "50a567c1-f216-4525-9341-9644c42b3193",
      "retrospective_step_id": "355e650f-a1e8-4d5e-b468-1e1e2d2e0bf0",
      "position": 1,
      "updated_at": "2025-09-18T09:21:23.593-07:00",
      "created_at": "2025-09-18T09:21:23.593-07:00"
    }
  }
}