Added new events to Phone Usage Manager.

[this-Aditya]

Fixes #430

[Hsankesara]

I am not sure if we should create new events or we could just label the rest of the events as Foreground, background or Interaction.

            FOREGROUND_SERVICE_START -> UsageEventType.FOREGROUND
            FOREGROUND_SERVICE_STOP -> UsageEventType.BACKGROUND
            STANDBY_BUCKET_CHANGED -> ?
            ACTIVITY_STOPPED -> UsageEventType.BACKGROUND

what do you think @yatharthranjan @blootsvoets ?

[blootsvoets]

I am not sure if we should create new events or we could just label the rest of the events as Foreground, background or Interaction

New event types are probably better. Foreground service means that there is something happening in the background that the user could be aware of via a notification. But no window or interaction is present. So that is why it was previously mapped to OTHER, we saw no big benefit in explicitly mapping it. But it's fine to do so anyway. Once the schema is merged, I'm fine with accepting this change.

[this-Aditya]

Sorry, I accidentally deleted it. I was deleting the branch locally, and the PR was automatically closed.