Add tests for RescueParty explicit health checks

RescueParty would trigger device config monitoring after initialization
of it's observer.
When the flags are updated, observer will receive callback for the same
and trigger explicit network health check with PackageWatchdog.
PackageWatchdog will inform RescueParty if the network check fails.

Bug: 397776123
Test: atest RescuePartyTest
Flag: com.android.crashrecovery.flags.flag_reset_enabled
Change-Id: Ib92b5e33a628a8b0433b2967b66f179f7213911c