use the new config to decide which service to use

Author: lucaspimentel

tracer/src/Datadog.Trace/Ci/TestOptimizationTracerManagerFactory.cs

@@ -107,7 +107,7 @@ protected override IAgentWriter GetAgentWriter(TracerSettings settings, IDogStat
             return new ApmAgentWriter(settings, updateSampleRates, discoveryService, traceBufferSize);
         }
 
-        protected override IDiscoveryService GetDiscoveryService(TracerSettings settings)
+        internal override IDiscoveryService GetDiscoveryService(TracerSettings settings)
             => _testOptimizationTracerManagement.DiscoveryService;
     }
 }

tracer/src/Datadog.Trace/TracerManagerFactory.cs

@@ -458,9 +458,6 @@ private static string GetUrl(TracerSettings settings)
             }
         }
 
-        protected virtual IDiscoveryService GetDiscoveryService(TracerSettings settings)
-            => DiscoveryService.Create(settings.Exporter);
-
         internal static IDogStatsd CreateDogStatsdClient(TracerSettings settings, string serviceName, List<string> constantTags, string prefix = null, TimeSpan? telemtryFlushInterval = null)
         {
             try
@@ -507,6 +504,11 @@ internal static IDogStatsd CreateDogStatsdClient(TracerSettings settings, string
             }
         }
 
+        internal virtual IDiscoveryService GetDiscoveryService(TracerSettings settings)
+            => settings.AgentFeaturePollingEnabled ?
+                   DiscoveryService.Create(settings.Exporter) :
+                   NullDiscoveryService.Instance;
+
         private static IDogStatsd CreateDogStatsdClient(TracerSettings settings, string serviceName)
         {
             var customTagCount = settings.GlobalTags.Count;