wifi: hotspot2: add Passpoint APIs to WifiManager

Add dedicated APIs for managing Passpoint configurations, since
Passpoint configurations are different from WiFi network
configurations.  A Passpoint configuration provides a credential for
authenticating to one or more WiFi networks that are operated
by the "same" service provider.

Bug: 32282711
Test: make -j32

Change-Id: I52822ab3074e2f2a3d986e3c0a24d024f2c06dca