[Contextual Edu] Enrich education logic

Add logic to
1. show 2 educations at most
2. show the 2nd education at least 7 days after 1st education

Bug: 354884305
Test: KeyboardTouchpadEduInteractorTest
Flag: com.android.systemui.keyboard_touchpad_contextual_education

Change-Id: Ie4f8abf6c9dfa230f16fe6dbcebd4169b14e8d8a