[BIC] Enable the creation of mock apps

We can populate mock background installed apps by setting the
value of "debug.transparency.bg-install-apps".
The string value is the list of names of the mock apps.

Bug: 266888785
Test: Run `adb shell setprop
      debug.transparency.bg-install-apps
      <some existing apps>`
      to set the list of mock apps.
      Run `adb shell cmd transparency get mba_info`
      to check existence of the apps.
Change-Id: I07a6106937a8217c16c31cbacf967d3c2102a2b1