The default webhook port does not work

[zhongduo]

Describe the bug

Kubernets adds additional env vars for each service with name
*_SERVICE_PORT, *_SERVICE_HOST and *_PORT, this causes trouble
in the webhook as it is using WEBHOOK_PORT to configure the
webhook port. Disabling it will enable using a default port.

Expected behavior
Without WEBHOOK_PORT env the default port should be used.
To Reproduce
remove the WEBHOOK_PORT env var in webhook.yaml and apply