Add new APIs to control modification of admin configured networks

* Historically, only the device owner could prevent the user from modifying
  networks that have been configured by the device owner.
* In New COPE mode, the COPE profile owner should now be able to prevent the
  user from modifying networks as well as the device owner.
* This CL adds new APIs which are callable by the device owner or profile
  owner of an organization-owned managed profile. These new API can be used
  to toggle the global setting WIFI_DEVICE_OWNER_CONFIGS_LOCKDOWN, instead of
  setting the global setting directly.
* This CL only affects networks configured by the admin, is does not prevent
  the user from creating more network configurations.

Bug: 147476790
Test: manual testing with TestDPC
      atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testAdminConfiguredNetworks
      atest com.android.cts.devicepolicy.OrgOwnedProfileOwnerTest#testAdminConfiguredNetworks

Change-Id: Ia16e639922bb08cdacd9a3766d978ac150b693c5