Support alternative domain names for webhooks.
Problem to solve
If you have an on-premise GitLab install you may have a separate domain for internal (LAN) access and a separate domain for external (WAN) access for security separation. This means that the configured domain for GitLab may differ from the domain used for external webhooks. When you configure Gitlab to integrate with an external service like Github, it uses the internal domain which is not accessible from the internet. This requires manually fixing webhook names whenever a new repo is integrated.
Allow specififying an alternative webhook URL that's used when configuring externally accessible webhooks (ie Github).
What does success look like, and how can we measure that?
Support the ability to configure alternative webhook domains for use with external integrations.