Add flag to control Internet preference

This CL adds a flag named config_show_internet_settings so access to
Internet preference can be easily customized as Wi-fi preference was in
the past, this level of customization was lost when Internet preference
was introduced here ag/13053253.

Bug: 271203982
Test: make -j32 Settings
Test: atest -c InternetPreferenceControllerTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:0af54a1d3cfa26ba5f23b5d8c74ade2bb582f76f)
Merged-In: Iaf9a18f9389be089304d11bd3206d6917ab85124

Change-Id: Iaf9a18f9389be089304d11bd3206d6917ab85124