Add "Use open Wi-Fi automatically" setting.

- Add constant in NetworkScoreManager for the meta-data key required
for NetworkRecommendationProviders to specify which package provides
this feature.
- Add Setting to specify which package is enabled for providing this
feature.

Bug: 34773276
Test: make
Change-Id: I3f8209c21b8b219c242650f97ba407b5985a5250