refactor: Implement MVVM approach for course dashboard

[farhan-arshad-dev]

Description

LEARNER-9215

• Implement MVVM approach for course dashboard
• Replace Loader Manager approach with MVVM + Coroutines(for Retrofit Requests).
• Remove CourseOutlineAsyncLoader in favour of Coroutine Scope.
• Remove multiple callbacks from the CourseOutline screen to handle error cases (ErrorHandlingCallbacks).

Inspirations Ref:

• https://developer.android.com/kotlin/coroutines/coroutines-best-practices
• https://medium.com/swlh/learn-by-doing-coroutines-a-guide-for-using-coroutines-in-android-for-retrofit-requests-eaef6ca58c7e

ps: doesn’t change behavior from the repo consumer perspective.