Add missing using directive

Author: mauroservienti

src/ServiceControl.Monitoring/HostApplicationBuilderExtensions.cs

@@ -22,6 +22,7 @@ namespace ServiceControl.Monitoring;
 using NServiceBus.Features;
 using NServiceBus.Transport;
 using QueueLength;
+using ServiceControl.Hosting;
 using Timings;
 using Transports;