Allowlist alarm-clock alarms from pre-S apps for FGS

FGS starts are allowed by default to apps targeting pre-S sdks. However,
on update their alarms may start getting denied if the app could not
reset its alarms.
Explicitly adding them to the allowlist to avoid this problem.

Test: atest FrameworksMockingServicesTests:AlarmManagerServiceTest
Test: Manual, using steps listed in b/238407723

Bug: 239098759
Bug: 238407723
Change-Id: I895901f0c870b161a8a4df92ebe93c873a55abc9