Add activity option flag for background starts for bubbles

Seems like something changed in udc that means we need this now.

A bubble only gets opened due to a user interaction so it should
be fine to use this flag.

Bug: 270058419
Test: manual - get an SMS bubble, tap on it, observe content loads
Change-Id: I6f8eaab793dc2fde45e097bbc1de38c995be02d6