[Android][Privacy Guide] Add user actions for MSBB change in PG

This CL adds two user actions "Settings.PrivacyGuide.ChangeMSSBOn"
and "Settings.PrivacyGuide.ChangeMSBBOff" to record the change of
the MSBB setting in Privacy Guide.

Bug: 1238896
Change-Id: I3206257b89a43f19679ea5701e2be71b18f30b08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4079112


Reviewed-by: Andrey Zaytsev <andzaytsev@google.com>
Commit-Queue: Filipa Senra <fsenra@google.com>
Cr-Commit-Position: refs/heads/main@{#1081421}