Mark session as ready on APEXd after verification

APEXd will now only verify packages when submitStagedSession is called,
and wait for an extra call from StagingManager when other verification
such us APK-container signature verification is performed.

Bug: 118865310
Bug: 123360647
Test: atest apex_e2e_tests; manual testing with packages with mismatched
APK signature

Change-Id: Ifa4d20b7d8ecbc25c8a6d9a41f92953cee374d35