Initial implementation of AccountSettings. (#6275)

* Make the UserPreference macro also generate an accessor for the key name.

* Initial implementation of AccountSettings.

- Add an AccountUserDefaults storage with a userID prefix on the key.
- Migrate the 2 values reset by AppSettings.resetSessionSpecificSettings to AccountSettings.

* Rename UserSettings.volatile() to UserSettings.mock()

Given it now has a userID parameter with a default value..

ElementX/Sources/Screens/CreateRoomScreen/View/CreateRoomScreen.swift

@@ -451,7 +451,7 @@ struct CreateRoom_Previews: PreviewProvider, TestablePreview {
                                       isSpace: Bool = false,
                                       selectionMode: CreateRoomScreenSpaceSelectionMode = .editableSpacesList(preSelectedSpace: nil),
                                       isAliasAvailable: Bool = true) -> CreateRoomScreenViewModel {
-        let userSettings = UserSettings.volatile()
+        let userSettings = UserSettings.mock()
         userSettings.knockingEnabled = isKnockingEnabled
         
         let clientProxy = ClientProxyMock(.init(userIDServerName: "example.org",

ElementX/Sources/Screens/CreateRoomScreen/View/CreateRoomSpaceSelectionSheet.swift

@@ -65,7 +65,7 @@ struct CreateRoomSpaceSelectionSheet_Previews: PreviewProvider, TestablePreview
         clientProxy.spaceService = SpaceServiceProxyMock(.init(editableSpaces: .mockJoinedSpaces2))
         let userSession = UserSessionMock(.init(clientProxy: clientProxy))
         
-        let userSettings = UserSettings.volatile()
+        let userSettings = UserSettings.mock()
         
         return CreateRoomScreenViewModel(isSpace: false,
                                          spaceSelectionMode: .editableSpacesList(preSelectedSpace: nil),