Introduce config_customBugreport option

This adds support for a custom bugreport handler. When the option is
enabled instead of immediately triggering the full bugreport, only a
CUSTOM_BUGREPORT_REQUESTED broadcast is sent.

Bug: 146052311
Test: built and tested locally
Change-Id: Ifea9906c15e0bc1281192a90b4dbdb0ad1ecfbdd