[5G settings UI] Add config for the 5G limited VoLTE alert dialog

Flag specifying whether to show an alert dialog for 5G disable
when the user disables VoLTE.

Bug: 151313654
Test: build pass. manual test: UI show alert dialog.
Change-Id: I5a5ab9e47722ad2ba28038233c5d2fc5fbe7e667
Merged-In: I5a5ab9e47722ad2ba28038233c5d2fc5fbe7e667