Add entrances for "Always-on VPN" and "Ignore battery optimizations" in settings

[Goooler]

We can add switchPreferences in AppSettingsScreen for the entrances:

• Enable them if the permissions are not granted / Disable if not.
• Click the switchPreference icon to request permissions or navigate to system Settings screens.

Refs:

• https://developer.android.google.cn/reference/android/provider/Settings#ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS
• https://developer.android.com/develop/connectivity/vpn#always-on