Enable and disable MSBB on history opt-in changes

This CL changes the way sync opt-in affects MSBB (aka in code as
URL-keyed data collection) for clients that have
`kReplaceSyncPromosWithSignInPromos` feature flag enabled. It does
not affect clients that are not in this experiment group.

For clients in this experiment, the CL enables and disables MSBB every
time user enables or disables history sync. This differs compared to the
previous implementation that relied on the sync opt-in in.

In the new implementation, `UnifiedConsentService` monitors all
changes to history opt-in and updates the state of the
UrlKeyedAnonymizedDataCollectionEnabled preference accordingly, so an
explicit call from the History opt-in UI is not needed anymore. This
is considered safe as history sync will be enabled only once the user
clicks "Yes" from the history opt-in screen and when the user toggles
the history toggle from the account settings.

Bug: 1462921
Change-Id: I4e7ddbaabb218cfe0083a853dd6b1218b385a9f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4669127
Commit-Queue: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1169314}