Option for "Notify only broken pipelines" with webhook integration
### Problem to solve
I would like a webhook that only fires when there is a build failure. Several of the integrations already offer this option (email, Slack, ...) but the standard webhook integration is all-or-nothing for pipeline events.
### Further details
My particular use case is sending notifications to Zulip, which uses the webhook functionality [docs](https://zulipchat.com/integrations/doc/gitlab); If I enable "Pipeline events" or "Job events" for a 3 stage pipeline this means at least 6 messages sent for every build. I would like to only hear about when the build has failed.
Build failures are important and it would be useful to have a webhook that is only fired for them.
### Proposal
Add "Notify only broken pipelines" option to webhooks.
### What does success look like, and how can we measure that?
"Notify only broken pipelines" option added to webhooks.
### Links / references
issue