Flag to fix cross-user avatar leak for avatar picker apps.

At the moment opening avatar picker app is based on action and category and possibly should be limited to a specific package to avoid opening malicious apps from settings.

Bug: 341688848
Change-Id: I11065adfcfdbc7fa5e59f889c7dd990e5b67bdd1
Flag: android.multiuser.fix_avatar_cross_user_leak
Test: N/A