Add 'Adaptive connectivity' UI

'Adaptive connectivity' toggle button controls whether
network connection is automatically managed.

Bug: 162871294
Test: make RunSettingsRoboTests
      manual
      Switch the toggle button and reboot device, observe
      if the state is retained.
Change-Id: I4499a3639abab356e8faa6316bfa45541efd63ac
Merged-In: I4499a3639abab356e8faa6316bfa45541efd63ac