feat(IAuthClient): IsConnected, ConnectionError und ConnectionError Eigenschaften hinzugefügt.

- Umwandlung der Eigenschaft IsConnectionFailed in eine Erweiterungsmethode.

DigitalData.Auth.Abstractions/IAuthClient.cs

@@ -2,6 +2,12 @@
 
 public interface IAuthClient : IAuthClientHandler
 {
+    bool IsConnected { get; }
+
+    Exception? ConnectionError { get; }
+
+    bool IsConnectionFailed => ConnectionError is not null;
+
     Task StartAsync();
 
     Task<bool> TryStartAsync();