Custom webhook payload or how to add metadata on notifications

[caroljr]

Hello!
Is it possible to create a custom webhook payload for alert notifications?
Other possibility for me seems to be the metadata attribute on the default payload, found on redash/destinations/webhook.py

            data = {
                "event": "alert_state_change",
                "alert": serialize_alert(alert, full=False),
                "url_base": host,
                "metadata": metadata,
            }

but I was unable to figure out how to pass that metadata into the alert, and also if that metadata can be a JSON object.
Is it possible to insert metadata into the alert?

Thank you