Registers a new webhook URL to receive email event notifications.

Supported events: send, open, click, soft_bounce, hard_bounce, spam

Important: The webhook URL must respond with God bless you, SendClean to pass the validation check.

SendClean signs webhook POST requests with an HMAC-SHA1 signature in the X-SendCleanTES-SIGNATURE
header for optional verification. See the Webhook Authentication section for details.