Bug fix flag to hide private space search illustration

Defines a flag based on which new config value is checked to either
show/hide the private space search illustration and search tile content
in Hide Private Space settings page.

Bug: 346612477
Test: Build
Flag: android.multiuser.private_space_search_illustration_config
Change-Id: Ie940e91f94f1df4e5dd57360c076a29ba6d6428e