Add new intent to signal that device customization is ready

Add a new intent to be broadcast when a new configuration has been
installed to signal that it is time to reboot the modem, refresh caches,
etc. To receive the intent, recipients must hold the new permission
"android.permission.RECEIVE_DEVICE_CUSTOMIZATION_READY".

This CL registers the intent, but does not send it: that is the
responsibility of the customization client, e.g. Phonesky. The sender is
expected to call PackageManager.sendDeviceCustomizationReadyBroadcast
and hold the new permission "android.permission.SEND_DEVICE_CUSTOMIZATION_READY".

Bug: 118462251
Test: manual (custom apps)
Change-Id: I9a723ca9ade16e8c5d316efbc7effd01e13ff2e7