add fan-out-fan-in sample

Signed-off-by: MregXN <mregxn@gmail.com>

examples/Workflow/WorkflowFanOutFanIn/Activities/NotifyActivity.cs

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+using Dapr.Workflow;
+using Microsoft.Extensions.Logging;
+
+namespace WorkflowFanOutFanIn.Activities
+{
+    public class NotifyActivity : WorkflowActivity<string, object>
+    {
+        readonly ILogger logger;
+
+        public NotifyActivity(ILoggerFactory loggerFactory)
+        {
+            this.logger = loggerFactory.CreateLogger<NotifyActivity>();
+        }
+
+        public override Task<object> RunAsync(WorkflowActivityContext context, string message)
+        {
+            this.logger.LogInformation(message);
+
+            return Task.FromResult<object>(null);
+        }
+    }
+}

examples/Workflow/WorkflowFanOutFanIn/Program.cs

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+using Dapr.Client;
+using Dapr.Workflow;
+using WorkflowFanOutFanIn.Activities;
+using WorkflowFanOutFanIn.Workflows;
+
+const string DaprWorkflowComponent = "dapr";
+
+var builder = Host.CreateDefaultBuilder(args).ConfigureServices(services =>
+{
+    services.AddDaprWorkflow(options =>
+    {
+        options.RegisterWorkflow<DemoWorkflow>();
+        options.RegisterActivity<NotifyActivity>();
+    });
+});
+
+
+DaprClient daprClient = new DaprClientBuilder().Build();
+
+// Wait for the sidecar to become available
+while (!await daprClient.CheckHealthAsync())
+{
+    Thread.Sleep(TimeSpan.FromSeconds(5));
+}
+
+using (daprClient)
+{
+    await daprClient.StartWorkflowAsync(
+    workflowComponent: DaprWorkflowComponent,
+    workflowName: nameof(WorkflowFanOutFanIn));
+
+}

examples/Workflow/WorkflowFanOutFanIn/WorkflowFanOutFanIn.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Dapr.Workflow\Dapr.Workflow.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <NoWarn>612,618</NoWarn>
+  </PropertyGroup>
+
+</Project>

examples/Workflow/WorkflowFanOutFanIn/Workflows/DemoWorkflow.cs

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+using Dapr.Workflow;
+using WorkflowFanOutFanIn.Activities;
+
+namespace WorkflowFanOutFanIn.Workflows
+{
+    public class DemoWorkflow : Workflow<string, string>
+    {
+        readonly WorkflowTaskOptions defaultActivityRetryOptions = new WorkflowTaskOptions
+        {
+            // NOTE: Beware that changing the number of retries is a breaking change for existing workflows.
+            RetryPolicy = new WorkflowRetryPolicy(
+                maxNumberOfAttempts: 3,
+                firstRetryInterval: TimeSpan.FromSeconds(5)),
+        };
+
+        public override async Task<string> RunAsync(WorkflowContext context)
+        {   
+            Console.WriteLine("Workflow Started."); 
+            Task<string> t1 =context.CallActivityAsync(nameof(NotifyActivity),"calling task 1 ...");
+            Task<string> t2 =context.CallActivityAsync(nameof(NotifyActivity),"calling task 2 ...");
+            Task<string> t3 =context.CallActivityAsync(nameof(NotifyActivity),"calling task 3 ...");
+            await Task.WhenAll(t1, t2, t3);
+
+            Console.WriteLine("Workflow Completed.");
+            return "Workflow Completed.";
+        }
+    }
+}