add onerr callback for leader elector (#1399)

Author: tg123

src/KubernetesClient/LeaderElection/LeaderElector.cs

@@ -28,6 +28,11 @@ public class LeaderElector : IDisposable
         /// </summary>
         public event Action<string> OnNewLeader;
 
+        /// <summary>
+        /// OnError is called when there is an error trying to determine leadership.
+        /// </summary>
+        public event Action<Exception> OnError;
+
         private volatile LeaderElectionRecord observedRecord;
         private DateTimeOffset observedTime = DateTimeOffset.MinValue;
         private string reportedLeader;
@@ -69,8 +74,9 @@ public async Task RunAsync(CancellationToken cancellationToken = default)
                                 MaybeReportTransition();
                             }
                         }
-                        catch
+                        catch (Exception e)
                         {
+                            OnError?.Invoke(e);
                             // ignore
                             return false;
                         }
@@ -129,6 +135,8 @@ private async Task<bool> TryAcquireOrRenew(CancellationToken cancellationToken)
                 {
                     return false;
                 }
+
+                OnError?.Invoke(e);
             }
 
             if (oldLeaderElectionRecord?.AcquireTime == null ||