Add config for Wi-Fi Hotspot Settings hidden

- Add config_show_wifi_hotspot_settings for Settings customization

- Hide Wi-Fi Hotspot preference in Hotspot & tethering Settings

- Don't launch Wi-Fi Hotspot Settings (e.g long press on Hotspot in QS-tile)

Bug: 213426762
Test: manual test
atest -c com.android.settings.wifi.WifiUtilsTest
make RunSettingsRoboTests ROBOTEST_FILTER=WifiTetherPreferenceControllerTest
make RunSettingsRoboTests ROBOTEST_FILTER=WifiTetherSettingsTest

Merged-In: I11f88d0d15d6d5c2766b64b5847ac31ed0f34c25
Change-Id: I11f88d0d15d6d5c2766b64b5847ac31ed0f34c25
(cherry picked from commit 160b5078)