[iOS] Enable OnSecurityEventEnterpriseConnector on iOS starting M137.

All reviews needed for dev/beta experiment have been approved in
https://launch.corp.google.com/launch/4374680.

Bug: 391860341
Change-Id: Ide570ed9f3a6f1a190f375ccdf91e2d2d8a79b12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6506563
Reviewed-by: Ernesto Izquierdo Clua <eic@google.com>
Reviewed-by: Nancy Xiao <nancylanxiao@google.com>
Commit-Queue: Xu Li <mxlg@google.com>
Reviewed-by: Salma Elmahallawy <esalma@google.com>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1454990}