Show policy transparency dialog if adding Wi-Fi config is not allowed

- When the user is restricted by UserManager.DISALLOW_ADD_WIFI_CONFIG, clicking on a Wi-Fi network will show the Settings policy transparency dialog.

- The "Not allowed by your organization" summary in Wi-Fi networks will be removed in a separate CL.

Bug: 233871529
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=Wifi

Change-Id: Ia978be8e85a5809de1331f3e0edc11fbc8925c80