Add a setting to control when to start glanceable hub.

To toggle the setting:

adb shell settings put secure when_to_start_glanceable_hub VALUE

Where a VALUE of 0 should disable auto-showing the hub.

Bug: 401001786
Test: NA (just declaring the setting in this change)
Flag: EXEMPT setting declaration
Change-Id: I27e520a6db32f172d63f5090453582b637492177