Update BTS Service to use push API instead of pull API in BIC

There will follow up CL to separate the handling of install and
uninstall events in BTS before we turn the flag on.

Host test and unit test will be added in a follow-up CL
(Bug: 374120984)

Flag: android.app.background_install_control_callback_api
Bug: 369382811
Test: manually testing
Change-Id: I91a7b45b027e8108888811f5be2b187b620513dd