Add ability to show/hide airplane toggle.

This introduces a new boolean flag:
config_show_toggle_airplane

Which when set to false, will hide the airplane mode toggle in network &
internet.

Bug: 69813881
Test: make RunSettingsRoboTests
ROBOTEST_FILTER=AirplaneModePreferenceControllerTest

Change-Id: I2cf682bf78231040eba5573fbcb55a65be2a13df