Add config to show an alert dialog for video charges

Add config to show an alert dialog for video charges when user starts
a video call. The default value is false.

Test: manual - Verified that a warning dialog about charges when a
video call is started if KEY_SHOW_VIDEO_CALL_CHARGES_ALERT_DIALOG_BOOL
is true.

Bug: 67832837
Test: manual
Change-Id: I11ab3ea9a8971a9d76b47714638f1fe0a9c980c2