Add writing function to intervention list

Create function to write game mode and game intervention
information to a file in known location. In the file we
write all the game packages installed by all users on
the device. We update/re-write the file when:

1. The user is switched
2. A game mode is changed
3. New device config is pushed and updated
4. Game mode/intervention is overriden via adb shell cmd

Bug: 219543620
Test: atest GameManagerServiceTests
Change-Id: I290f9b72d4654c7308797686a5e37d5887369d8d