Add SamplingService

src/SkyWalking.Core/Sampling/SamplingService.cs

+using System.Threading.Tasks;
+
+namespace SkyWalking.Sampling
+{
+    public class SamplingService : ISampler
+    {
+        public Task Executing()
+        {
+            return Task.CompletedTask;
+        }
+
+        public Task Executed()
+        {
+            return Task.CompletedTask;
+        }
+
+        public bool TrySampling()
+        {
+            return true;
+        }
+
+        public void ForceSampled()
+        {
+        }
+    }
+}
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