NotificationsScreen: Create fake ViewModel and interface

[takahirom]

What needs to be done

• Model classes
• UI can use the ViewModel's fake data
• Provide FakeViewModel in ProvideViewModels
• Add test

Reference

• https://github.com/DroidKaigi/droidkaigi-feed-reader-app/blob/3a633f81692a8a1ef9dd[...]ithub/droidkaigi/feeder/contributor/FakeContributorViewModel.kt
• https://github.com/DroidKaigi/droidkaigi-feed-reader-app/blob/d049d5951d88f8c40402[...]/io/github/droidkaigi/feeder/viewmodel/ProvideRealViewModels.kt
• Test https://github.com/DroidKaigi/conference-app-2021/blob/9dadaa78d98bd5913c22efb9afd[...]st/java/io/github/droidkaigi/feeder/ContributorViewModelTest.kt

[takahirom]

API response https://github.com/DroidKaigi/droidkaigi-feed-reader-app/issues/8