[Wi-Fi] Add button in WifiEntryPreference for launching OpenRoaming help page

Add button resource in WifiEntryPreference for launching OpenRoaming help page, shows according to the canManageSubscription API return true or not.

Bug: 146669261
Test: Add canManageSubscription_shouldSetImageButtonVisible unit test to check if button shows correctly or not.
Change-Id: I0becac9b15b5be3d4f9e5a9089cfd83652824789
5 files changed