fix(mobile): hide latest version warnings (#26036)

The latest version is already hidden in the server info widget if
disabled (https://github.com/immich-app/immich/pull/25691), however I
did not realise there are more places where this warning is shown. This
hides the warning everywhere, and cleans up the code a bit.

mobile/lib/models/server_info/server_info.model.dart

@@ -28,7 +28,7 @@ class ServerInfo {
 
   const ServerInfo({
     required this.serverVersion,
-    required this.latestVersion,
+    this.latestVersion,
     required this.serverFeatures,
     required this.serverConfig,
     required this.serverDiskInfo,