Add new class for WiFi restractions caching

- Create a singleton class for Wi-Fi restricted caching.

- Manages mapping between user ID and corresponding singleton object.

- Add new isConfigWifiAllowed() function.

Bug: 202017876
Test: manual test
make RunSettingsLibRoboTests ROBOTEST_FILTER=WifiRestrictionsCacheTest

Change-Id: Ieaa90f170cf679ec00cc752e5af173d151296c89