[Gallery] Move Sample Preference to sub page

Will add more preferences later.

Also upgrade AGP version to 7.3.0-rc01, to work with Android Studio
Dolphin | 2021.3.1 RC 1

Bug: 235727273
Test: Manual with Gallery App
Change-Id: I426830ac698185c27362c1b7d48d076d7a30f3f2