Update documentation of ApnSetting with V5 example

ApnSetting#fromString has had 2 version bumps since the documentation
was written. Users of the resource overlay can mix and match versions,
so this documentation gives an example of a V5 format ApnSetting with a
V3 one.

Bug: 70172263
Test: manual; no behavior change
Change-Id: I20ff199fb60304fbb7c2a8b837869bfd143eba16
Merged-In: I20ff199fb60304fbb7c2a8b837869bfd143eba16