[CS][Disable] Add DisableFlagsRepo and use it for notif alerts status.

Bug: 287076786
Test: manual: When DISABLE_NOTIFICATION_ALERTS comes through
CommandQueue, verify that repo and StatusBarNotificationPresenter get
the right value
Test: manual: When DISABLE_NOTIFICATION_ALERTS is on, send notif ->
verify it doesn't HUN
Test: manual: When DISABLE_NOTIFICATION_ALERTS is off, send notif ->
verify it *does* HUN
Test: `adb shell dumpsys activity service
com.android.systemui/.SystemUIService DisableFlagsRepository` -> dumps
disable flags

Test: atest DisableFlagsRepositoryTest
Test: atest NotificationsInteractorTest
StatusBarNotificationPresenterTest

Change-Id: I44eb2da2ab88bc0d007b7cc913396f0f7f2c257f