Fix IP whitelist link re: moving to allowlist

The issue that was linked previously has been replaced by an epic, which
this now links to.

doc/administration/monitoring/ip_whitelist.md

@@ -9,7 +9,7 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 > Introduced in GitLab 9.4.
 
 NOTE:
-We intend to [rename IP whitelist as `IP allowlist`](https://gitlab.com/gitlab-org/gitlab/-/issues/7554).
+We intend to [rename IP whitelist as `IP allowlist`](https://gitlab.com/groups/gitlab-org/-/epics/3478).
 
 GitLab provides some [monitoring endpoints](../../user/admin_area/monitoring/health_check.md)
 that provide health check information when probed.