Relaxing minimum alarm window requirements

Minimum allowed window is now a function of the futurity of the alarm.
So for alarms in the near future, it is smaller and it increases as time
to alarm increases maxing out at 10 minutes.

Test: atest AlarmManagerServiceTest

Bug: 185199076
Change-Id: I57f275adab7f9bcc7f0f7535bb810aa9b359287b