Restrict ApnEditor settings

- Finish ApnEditor settings if user is not an admin

- Finish ApnEditor settings if user has DISALLOW_CONFIG_MOBILE_NETWORKS restriction

Bug: 279902472
Test: manual test
atest -c ApnEditorTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4e18e7414c674a1c5bc69961c03499849b4aefd2)
Merged-In: Iecdbbff7e21dfb11e3ba385858747a220cfd3e04
Change-Id: Iecdbbff7e21dfb11e3ba385858747a220cfd3e04