Onboarding flow refactor (EXPOSUREAPP-2995) (#1337)

* Added MVVM and DI to OnboardingFragment

* Refactored OnboardingFragment to work with MVVM and DI

* Refactored OnboardingPrivacyFragment to work with MVVM and DI

* Moved navigation functions from OnboardingTracingFragment to VM

* Refactored OnboardingTestFragment to work with MVVM and DI

* Refactored OnboardingNotificationsFragment to work with MVVM and DI

* Added ktlintFormat changes

* Added intstrumentation tests skeleton for each fragment in Onboarding flow

* Removed unused import

* Changed Onboarding fragment top constraint

* Removed unnecessary VM declaration from layouts

* Added requested changes

* Added new lineat end of files

Co-authored-by: harambasicluka <64483219+harambasicluka@users.noreply.github.com>
Co-authored-by: Matthias Urhahn <matthias.urhahn@sap.com>
Co-authored-by: Ralf Gehrer <ralfgehrer@users.noreply.github.com>