URL validation for custom webhooks does not work with docker services networking

[youtous]

Hi,

Thank you for this kibana plugin!

I'm using a webhook processor in a container, I would like to be able to query the webhook service using it's name: http://webhook:8080/email or with http://webhook/email.

validateHost does not permits this (frontend validation).

Workaround

POST _opendistro/_alerting/destinations
{
  "name": "smtp",
  "type": "custom_webhook",
  "custom_webhook": {
    "url": "http://webhook-smtp:8080/email"
  }
}