Add OEM_PAID capability to system api

Some system apps should be able to request OEM_PAID networks.  This
makes a lot of sense when Android is used as in-vehicle infotainment
systems.

Bug: 68762530

Test: runtest -x frameworks/base/tests/net/ -c android.net.NetworkCapabilitiesTest

Change-Id: Ic916de7522a9f803a2410bc4e3e82101fd9d0dbd