[Contextual Edu] Make contextual education module optional

Removed depedency of ContextualEducationModule in OverviewProxyService.
Removed contextual education from SystemUIModule and added it to ReferenceSystemUIModule.
More detail in go/contextual-edu-module-optional.

Moved the update logic from KeyboardTouchpadEduStatsInteractor to KeyboardTouchpadEduInteractor as it will listen to updates from OverviewProxyService when application starts using CoreStartable.

Bug: 372201176
Test: KeyboardTouchpadEduInteractorTest
Flag: com.android.systemui.keyboard_touchpad_contextual_education
Change-Id: I3f141b3e032d0563dbb15f4fbcefe2f4be85f9b8