Add traces around updateZenModeConfig

From field traces, it seems it often requires a lot of time (>190ms during LOCKSCREEN_TO_AOD CUJ) due to lock contention in the binder calls happening inside.

Adding a slice to make it more recognizable

Bug: 289485377
Test: Record Perfetto trace - check the new slice is visible
Change-Id: I77a662d17237246d8c9f2c06b38b5bfa64d5c69d