p2p: add WifiP2pConfig builder for new API

Creating/Joining a group with credentials needs additional
fields in WifiP2pConfig. Using builder to construct corresponding
WifiP2pConfig object

Bug: 64695709
Test: Unit tests - atest frameworks/opt/net/wifi/tests/wifitests
Change-Id: Ib01a7a1313fab3a7e3e9a0c6c9a10e419deed9d4