Create Slack trigger

curl --request POST \
  --url https://app.langwatch.ai/api/triggers/slack \
  --header 'Content-Type: application/json' \
  --header 'X-Auth-Token: <api-key>' \
  --data '{
  "slack_webhook": "<string>",
  "name": "<string>",
  "message": "<string>",
  "filters": {
    "metadata.user_id": [
      "<string>"
    ],
    "metadata.thread_id": [
      "<string>"
    ],
    "metadata.customer_id": [
      "<string>"
    ],
    "metadata.labels": [
      "<string>"
    ],
    "metadata.custom_value": {}
  },
  "alert_type": "ERROR"
}'