[WifiTrackerLib] Implement manual and auto captive portal opening

Allow the user to sign in to captive portals through the wifi picker.
The captive portal app will also auto-open on the wifi picker page and
the Network Details page following a manual user connection to the
network.

Bug: 70983952
Bug: 149354973
Test: manual verification with local captive portal AP, atest
WifiTrackerLibTests

Change-Id: I9311bf38b861715c74b6415204ef63eab70ab717
6 files changed