PrivacySandboxPrefs to set addToBackStack to true

This change updates prefs extending PrivacySandboxSettingsBaseFragment
to set the argument `addToBackStack` to true. So that when a back press
event takes place on a pref launched using this method, it goes back to
the previous view rather than exiting completely to the main settings
view.

Bug: 474422494
Change-Id: Ic1d704c2516b374f92e65a73266355363ab15596
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7476082
Reviewed-by: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Moe Adel <adelm@google.com>
Cr-Commit-Position: refs/heads/main@{#1569808}