Configure the AuthenticationService later now that we have 2 flows on the start screen. (#3316)

* Don't query the homeserver until confirming it (or selecting a different one).

* Setup the infrastructure to test AuthenticationService.

Implement basic tests for configuration & password login.

* Use the real AuthenticationService with a mock Client in all of the tests.

* Add tests for the ServerConfirmationScreenViewModel.

* Remove redundant view state and test for it.

UnitTests/Sources/ServerSelectionViewModelTests.swift

@@ -16,8 +16,7 @@ class ServerSelectionViewModelTests: XCTestCase {
     
     @MainActor override func setUp() {
         viewModel = ServerSelectionScreenViewModel(homeserverAddress: "",
-                                                   slidingSyncLearnMoreURL: ServiceLocator.shared.settings.slidingSyncLearnMoreURL,
-                                                   isModallyPresented: true)
+                                                   slidingSyncLearnMoreURL: ServiceLocator.shared.settings.slidingSyncLearnMoreURL)
         context = viewModel.context
     }