Creates a sub-status assignment

curl --request POST \
  --url https://api.rootly.com/v1/incidents/{incident_id}/sub_statuses \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '
{
  "data": {
    "type": "incident_sub_statuses",
    "attributes": {
      "sub_status_id": "<string>",
      "assigned_at": "<string>",
      "assigned_by_user_id": 123
    }
  }
}
'

{
  "data": {
    "id": "<string>",
    "type": "incident_sub_statuses",
    "attributes": {
      "incident_id": "<string>",
      "sub_status_id": "<string>",
      "assigned_at": "<string>",
      "assigned_by_user_id": 123
    }
  }
}