Add option to not automatically disable webhooks on failure

Currently, webhooks are disabled automatically after 25 failures. For webhooks listening to common events like document.update, this threshold is reached very quickly, if the connection between Outline and the webhook target fails for some reason.
Thus, temporary failures in the connection between these components (which happen from time to time, particularly in Intranets) usually result in a permanent outage of the webhook, which has to be fixed manually.

Please add an option to disable this behavior of automatically disabling webhooks either globally or per webhook.

I understand the intention of wanting to save resources by not sending messages to broken webhooks, but particularly in self hosted instances, quick recovery from failure conditions matters a lot more than wasted computing.