Add WiFi Enterprise restrictions check for WiFi Configuration Addition

  When UserManager.DISALLOW_ADD_WIFI_CONFIG is set to true.
  - Disable the "Add network" item in the Internet settings.

  - Activity action API for ACTION_WIFI_ADD_NETWORKS should not be
    permitted and the user shouldn’t see a prompt for approval

Bug: 203169077
Test: make RunSettingsRoboTests ROBOTEST_FILTER=NetworkProviderSettingsTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=AddAppNetworksActivityTest
Change-Id: I18d7703b5972bfbc12dca10b6432d756813abace