feat: add reload semantics for cluster and jetstream options

src/NATS.Server/NatsServer.cs

@@ -1025,10 +1025,22 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
     /// the changes, and applies reloadable settings. CLI overrides are preserved.
     /// </summary>
     public void ReloadConfig()
+    {
+        ReloadConfigCore(throwOnError: false);
+    }
+
+    public void ReloadConfigOrThrow()
+    {
+        ReloadConfigCore(throwOnError: true);
+    }
+
+    private void ReloadConfigCore(bool throwOnError)
     {
         if (_options.ConfigFile == null)
         {
             _logger.LogWarning("No config file specified, cannot reload");
+            if (throwOnError)
+                throw new InvalidOperationException("No config file specified.");
             return;
         }
 
@@ -1054,6 +1066,8 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
             {
                 foreach (var err in errors)
                     _logger.LogError("Config reload error: {Error}", err);
+                if (throwOnError)
+                    throw new InvalidOperationException(string.Join("; ", errors));
                 return;
             }
 
@@ -1065,6 +1079,8 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         catch (Exception ex)
         {
             _logger.LogError(ex, "Failed to reload config file: {ConfigFile}", _options.ConfigFile);
+            if (throwOnError)
+                throw;
         }
     }