Settings: Create aconfig flag for search result deep links in same task

This will be used to guard the bugfix a bug where the deep link
initiated from a search result would open the results page in a separate
window.

Bug: 381127948
Test: None
Flag: com.android.settings.flags.settings_search_result_deep_link_in_same_task
Change-Id: I5a10df558130176ae9df39c0c35501def948430d