Add Epic events webhook

Rationale

As a user, I develop automations & bots around GitLab. We are using the Epics heavily and I cannot get any notifications on Epic description changes or status changes (labels, assignees...).

I simply need a webhook for Epics events. I am using Gitlab 14.6, as an ultimate customer. This issue shall go into &2318 (closed), after discussion with Gitlab Support.

Thanks.

Customer Demand

• Ultimate, 42 seats
• Ultimate prospect
• Premium, 110 seats