Add a feature flag for spaces. (#4429)

* Remove the huge conditional compilation block on AppSettings.

It is still required for the ElementCallBaseURL however.

* Add a feature flag for spaces.

ElementX/Sources/Screens/Settings/DeveloperOptionsScreen/DeveloperOptionsScreenModels.swift

@@ -42,6 +42,7 @@ protocol DeveloperOptionsProtocol: AnyObject {
     var enableOnlySignedDeviceIsolationMode: Bool { get set }
     var enableKeyShareOnInvite: Bool { get set }
     var threadsEnabled: Bool { get set }
+    var spacesEnabled: Bool { get set }
     var hideQuietNotificationAlerts: Bool { get set }
     
     var hideUnreadMessagesBadge: Bool { get set }