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": "<string>",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "<string>",
      "retrospective_step_id": "<string>",
      "position": 123
    }
  }
}