Relax WiFi cert installation restrictions in HSUM mode

The Settings app runs under the current user, which previously lacked
the necessary permissions to install client certificates in HSUM mode.

This change allows any admin user to install these certificates.

Bug: b/370013519
Flag: EXEMPT bugfix
Test: manually installed and removed client certificate for WiFi
Change-Id: I57a7364c76a0adb7ed4112e48fb20070ab9d7bff