Add a default apn-conf.xml into GSI

Add a default apn-conf.xml for telephony data network, then some
devices, ex. emulator, could use the default setting when it's
system image overrided by GSI.

Bug: 69869274
Test: build pass and boot a Pixel device with GSI to home screen
Change-Id: I0275a5d420eadcbb2f744e995c9a72a1fb46b935