personalization: Add metric for keyboard backlight display type

Add a new metric
"Ash.Personalization.KeyboardBacklight.DisplayType.Settled" to
record the display type of keyboard backlight color that the user has
settled on.

BUG=b:274961222
Test=Set keyboard backlight color as a static color. Verify that
the value in
shows correctly after UMA upload for the day.
TEST=Set the keyboard backlight color with customized zones. Repeat the
histogram verification step.

chrome: //histograms/Ash.Personlization.KeyboardBacklight.Display.Settled
Change-Id: I0121f25cd58b3b3526aef638143deafc6bdc844b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4375042


Reviewed-by: Jason Thai <jasontt@chromium.org>
Commit-Queue: Thuong Phan <thuongphan@chromium.org>
Reviewed-by: Yulun Wu <yulunwu@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1123743}