Allow TraceSessionEnded reporting to be muted.

This will allow System UI's Issue Recording QS tile to start and stop
long traces.

Bug: 343538743
Test: Verified manually on device that the crash and the notification no
longer appear for long traces that have been stopped.
Flag: EXEMPT bug fix

Change-Id: If127aef17872a9fab54a916f008174e71b4cff6c