Improve discoverability of the intent & actions progress

- Display "Select the network you want to use for data" on sub-title
when Wi-Fi networks is not empty

- Screenshot:
  https://screenshot.googleplex.com/6nuwYoSh7UjF93Q

Bug: 186432232
Test: manual test
atest -c InternetConnectivityPanelTest

Change-Id: I9ab0ce0ca052b3444e50a914b59f38e4e7778ddf