Allow Users to migrate their hotseat when returning from AiAi

- If a user has mostly predicted hotseat, show a snack bar. otherwise, show migration option.
- Guard onboarding activity with permission `com.google.android.apps.nexuslauncher.permission.HOTSEAT_EDU`

Bug: 158569583
Test: Manual
Change-Id: Id0c1c812233fcf288a2f49848720199dedd2015d