Add a flag to fix the null pointer exception on Avatar Picker.

When the content provider authority is null. Avatar Picker takes first content provider with an intent filter. This can cause an issue when another provider has the same filters. Fix will keep authority in resources.

Bug: 362880068
Change-Id: Ic2e6175d0587278155d7281ddcc86c4c17087dac
Flag: android.multiuser.fix_avatar_content_provider_null_authority
Test: N/A