Group stream joined event

{
  "groupId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "streamId": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "subject": "<string>",
  "streamSubject": "<string>",
  "dynamicWebhookEndpoints": [
    {
      "id": "<string>",
      "url": "<string>",
      "events": [
        "<string>"
      ],
      "enabled": true,
      "description": "<string>"
    }
  ]
}