[NetworkSuggestion] add API to allow app share credential with user

When app shares credential with user that suggestion will show in the
WifiPicker. And user can click to connect to that network.

Bug: 142134651
Test: atest android.net.wifi
Test: atest com.android.server.wifi
Change-Id: I1d64abdd045734f4f79a4424f4f6199d7e6cd7d2