[Wi-Fi] Sync Connect button UI with WifiEntry connected state

The Connect button in the Network Details Page should be synced to the
connected state of WifiEntry and should toggle between not visible,
"Connect", and "Connecting..." accordingly.

Bug: 70983952
Test: manual - connect to in-range saved network through Network Details
page

Change-Id: Id34a840dd81fb99c8e64ad219b0b7af73946c1bf