Epic: create and join rooms - Start Chat (#680)

* add start chat flow with UI

* add feature flag for start chat

* add changelog

* fix naming and tests

* fix empty display name in user cell

* Update ElementX/Sources/Application/AppSettings.swift

Co-authored-by: Alfonso Grillo <alfogrillo@element.io>

* add screenshots from UI test

* fix swiftFormat and add identifiers

* fix warnings

---------

Co-authored-by: Alfonso Grillo <alfogrillo@element.io>

ElementX/Sources/Application/AppSettings.swift

@@ -27,6 +27,7 @@ final class AppSettings: ObservableObject {
         case enableInAppNotifications
         case pusherProfileTag
         case shouldCollapseRoomStateEvents
+        case showStartChatFlow
     }
     
     private static var suiteName: String = InfoPlistReader.main.appGroupIdentifier
@@ -140,7 +141,7 @@ final class AppSettings: ObservableObject {
     
     @UserSetting(key: UserDefaultsKeys.shouldCollapseRoomStateEvents.rawValue, defaultValue: true, persistIn: nil)
     var shouldCollapseRoomStateEvents
-
+    
     // MARK: - Notifications
 
     @UserSetting(key: UserDefaultsKeys.timelineStyle.rawValue, defaultValue: true, persistIn: store)
@@ -153,4 +154,11 @@ final class AppSettings: ObservableObject {
     // MARK: - Other
     
     let permalinkBaseURL = URL(staticString: "https://matrix.to")
+    
+    // MARK: - Feature Flags
+    
+    // MARK: Start Chat
+    
+    @UserSetting(key: UserDefaultsKeys.showStartChatFlow.rawValue, defaultValue: false, persistIn: store)
+    var startChatFlowFeatureFlag
 }