adding go-plugin example using C#

examples/grpc/plugin-dotnet/.gitignore

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+bin
+obj
+go-plugins

examples/grpc/plugin-dotnet/HealthService.cs

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+using Grpc.Core;
+
+namespace plugin_dotnet
+{
+    public static class HealthService
+    {
+        public static IHealthService Get() =>
+            new Grpc.HealthCheck.HealthServiceImpl();
+
+        public static ServerServiceDefinition BindService(IHealthService health) =>
+            Grpc.Health.V1.Health.BindService((Grpc.Health.V1.Health.HealthBase)health);
+    }
+
+    public interface IHealthService
+    {
+        void ClearAll();
+        void ClearStatus(string service);
+        void SetStatus(string service, HealthStatus status);
+
+
+    }
+
+    public enum HealthStatus
+    {
+        Unknown = 0,
+        Serving = 1,
+        NotServing = 2,
+    }
+}

examples/grpc/plugin-dotnet/Plugin.cs

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+
+using System;
+using System.IO;
+using System.Threading.Tasks;
+using Google.Protobuf;
+using Grpc.Core;
+using Proto;
+
+namespace plugin_dotnet
+{
+    class Plugin : KV.KVBase
+    {
+        public const string ServiceHost = "localhost";
+        public const int ServicePort = 1234;
+        public const int AppProtoVersion = 1;
+
+        public override async Task<Empty> Put(PutRequest request, ServerCallContext context)
+        {
+            var filename = $"kv_{request.Key}";
+            await File.WriteAllTextAsync(filename,
+                $"{request.Value.ToStringUtf8()}\n\nWritten from plugin-dotnet\n");
+
+            return new Empty();
+        }
+
+        public override async Task<GetResponse> Get(GetRequest request, ServerCallContext context)
+        {
+            var filename = $"kv_{request.Key}";
+            return new GetResponse
+            {
+                Value = ByteString.CopyFromUtf8(await File.ReadAllTextAsync(filename)),
+            };
+        }
+
+        static async Task Main(string[] args)
+        {
+            // go-plugin semantics depend on the Health Check service from gRPC
+            var health = HealthService.Get();
+            health.SetStatus("plugin", HealthStatus.Serving);
+
+            // Build a server to host the plugin over gRPC
+            var server = new Server
+            {
+                Ports = { { ServiceHost, ServicePort, ServerCredentials.Insecure } },
+                Services = {
+                    { HealthService.BindService(health) },
+                    { KV.BindService(new Plugin()) },
+                },
+            };
+
+            server.Start();
+
+            // Part of the go-plugin handshake:
+            //  https://github.com/hashicorp/go-plugin/blob/master/docs/guide-plugin-write-non-go.md#4-output-handshake-information
+            await Console.Out.WriteAsync($"1|1|tcp|{ServiceHost}:{ServicePort}|grpc\n");
+            await Console.Out.FlushAsync();
+
+            while (Console.Read() == -1)
+                await Task.Delay(1000);
+
+            await server.ShutdownAsync();
+        }
+    }
+}